单选题In the late 1930's and early 1940's, Jacob Lawrence created many paintings _________ the lives of famous African American activists.

单选题The author mentions twenty percent itl line 23 to indicate that

单选题The word "it" in line 22 refer to

单选题All of the following are defined in the passage EXCEPT

单选题The word "They" in line 24 refers to

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单选题------subject to rust, many examples of decorative ironwork on buildings have disappeared.

单选题At its center, the sun has a density of over a hundred times ________and a temperature of 10 to 20 million degrees centigrade.

单选题According to paragraph 3, which of the following is most important for an effective survey?

单选题According to the passage, the meaning of a message communicated through a pheromone may vary when the

单选题The word "alert" in line 13 is closest in meaning to

单选题The word "sustain" in line 6 is closets in meaning to

单选题According to the passage, how did the shift to agricultural societies impact people's family relationships?

单选题According to the passage, an advantage of using a photoflash is that it

单选题True cedars are (members) of the pine family and are 120 to 150 (feet tall), with (erect )cones and (bunches short), needlelike leaves.

单选题During the years he composed, Charles Ives was isolation from the music world; none of his major works was publicly performed.

单选题Panama Canal The 50.7-mile long Panama Canal was completed in 1914 with three locks on the Pacific and Atlantic sides. It was first conceived by the Spanish in 1524 when King Charles V ordered a survey of the construction of a waterway across the isthmus. The Panamanians ultimately gained their independence from Spain and it was not until 1880, when Panama was under control of Columbia, that construction was actually attempted. The Colombian government granted the construction concession to the French Canal Company, whose attempt at construction of a sea level canal ended in bankruptcy nine years later. The rights and assets of the canal were subsequently purchased by the United States for $40 million in 1903, when Panama, with U.S. backing, declared its independence from Columbia. The U.S. paid Panama $I0 million and $250,000 each year for use of the canal. This yearly sum was tipped in 1933 and 1955, and, in exchange, the U.S. was given control of the Canal Zone, a ten mile strip across the isthmus, as well as substantial influence in Panamanian affairs. In 1977, two treaties were negotiated between the U.S. and Panama to return control of the Canal to Panama. One treaty governs the transfer of the Canal, and the other governs its neutrality following transfer. The Panamanian people approved the treaties by referendum in 1977, and the following year the U.S. Senate gave its approval. The treaties turned control of the canal over to Panama on December 31, 1999. According to the treaties, while the U.S. will relinquish control of the Panama Canal, it may intervene with military force to keep the Canal open if it were to become obstructed. The construction of the Panama Canal was determined by economical and political reasons. The French"s intention was to exert control over their Caribbean colonies by facilitating access towards French Guyana, which was located at the Northern tip of the South American Continent. Later, the USA wanted to lay territorial claim over the autonomous regions of Puerto Rico and El Salvador, which bordered Panama. They wrestled control of the canal away from Panama and managed to dictate terms in political treatise by closing the canal to commercial traffic and effectively instituting an economic embargo over nations whose commerce depended on navigating its waters. At the time of its opening, the Panama Canal was the largest construction of its kind connecting two bodies of water, the Pacific and the Atlantic Ocean. Only the 1869 Suez Canal that was to connect the Red Sea with the Mediterranean would surpass it in length. 18,000 people lost their lives while toiling at the erection of the Panama Canal, most fatalities having resulted from drowning. Today, the Panama Canal is open to maritime traffic to any commercial or private vessel for a certain fee. Traversing the canal halves the distance between the Atlantic and the Pacific and results in considerable financial and time savings. Glossary isthmus: a narrow strip of land connecting two larger masses of land concession: a contract granting the right to operate a subsidiary business strip: a long narrow region of land or body of water referendum: the submission of a proposed public measure

单选题1 Several men have been responsible for promoting forestry as a profession. Foremost was Gifford Pinchot, the father of professional forestry in America. He was chief of the Forest Service from 1898 until 1910, working with President Theodore Roosevelt to instigate sound conservation practices in forests. Later he was professor of forestry and founder of the Pinchot School of Forestry at Yale University. Another great forester was Dr. Bernard E. Fernow, the first head of the U.S. Forest Service. He organized the first American school of professional forestry at Cornell University. 2 The foresters of today, like Pinchot and Fernow in the past, plan and supervise the growth, protection, and utilization of trees. They make maps of forest areas, estimate the amount of standing timber and future growth, and manage timber sales. They also protect the trees from fire, harmful insects, and disease. Some foresters may be responsible for other duties, ranging from wildlife protection and watershed management to the development and supervision of camps, parks, and grazing lands. Others do research, provide information to forest owners and to the general public, and teach in colleges and universities.

单选题The word "Accordingly" in line 24 is closest in meaning to