单选题There are no solitary, free-living creature; every form of life is ______ other form.

单选题The reader can conclude that the Parthenon ______.

单选题The Untied States and Canada are lands of ______ except for the Indians, who are the only true natives.

单选题The headlights of the approaching car were so ______ that the cyclist had to stop riding. A.gleaning B.staring C.gleaming D.dazzling

单选题{{B}}Passage 2{{/B}} The two claws of the mature American lobster are decidedly different from each other. The crusher claw is short and stout; the cutter claw is long and slender. Such bilateral asymmetry, in which the fight side of the body is, in all other respects, a mirror image of the left side, is not unlike handedness in humans. But where the majority of humans are right-handed, in lobsters the crasher claw appears with equal probability on either the right side or left side of the body. Bilateral asymmetry of the claws comes about gradually. In the juvenile fourth and fifth stages of development, the paired claws are symmetrical and cutter like. Asymmetry begins to appear in the juvenile sixth stage of development, and the paired claws further diverge toward well-defined cutter and crusher claws during succeeding stages. An intriguing aspect of this development was discovered by Victor Emmer. He found that if one of the paired claws is removed during the fourth or fifth stage, the intact claw invariably becomes a crusher, while the regenerated claw becomes a cutter. Removal of a claw during a later juvenile stage or during adulthood, when asymmetry is present, does not alter the asymmetry; the intact and regenerate claws retain their original structures. These observations indicate that the conditions that trigger differentiation must operate in a random manner when the paired claws are intact, but in a nonrandom manner when one of the claws is lost. One possible explanation is that differential use of the claws determines their asymmetry. Perhaps the claw that is used more becomes the crusher. This would explain why, when one of the claws is missing during the fourth or fifth stage, the intact claw always becomes a crusher. With two intact claws, initial use of one claw might prompt the animal to use it more than the other throughout the juvenile fourth and fifth stages, causing it to become a crusher. To test this hypothesis, researchers raised lobsters in the juvenile fourth and fifth stages of development in a laboratory environment in which the lobsters could manipulate oyster chips. (Not coincidentally, at this stage of development lobsters typically change from a habitat where they drift passively, to the ocean floor where they have the opportunity to be more active by borrowing in the substrate.) Under these conditions, the lobsters developed asymmetric claws, half with crusher claws on the left, and half with crusher claws on the right. In contrast, when juvenile lobsters were reared in a smooth tank without the oyster chips, the majority developed two cutter claws. This unusual configuration of symmetrical cutter claws did not change when the lobsters were subsequently placed in a ma nipulable environment or when they lost and regenerated one or both claws.

单选题The captain performs his duties with great ______ and all the crew believed that they can get over the storm. A. affection B. suspicion C. assurance D. definition

单选题The gang derived their nickname from their dark clothing and blacked up faces for nocturnal raids in the forest.

单选题Good writers are often also ______ readers who enjoy equally fiction and nonfiction, prose and poetry, philosophy and science. A. carnivorous B. omnivorous C. herbivorous D. prestigious

单选题What is true about Henry Louis "Skip" Gates Jr.?

单选题The phrase "vocal... exponent" (line 2, paragraph 5) most probably refers to______.

单选题I was ______ by their kindness and moved to tears.

单选题Attitudes on the two sides in the Revolutionary War {{U}}precluded{{/U}} the possibility of a peaceful solution.

单选题All of us were______ that the old man could walk on his hands.

单选题______ John I began to trust my feelings and began to believe in my ability. A. Due to B. Obliged to C. By virtue of D. Thanks to

单选题Finding ways of helping Russia ______ its upheavals will be the most pressing task.

单选题In recent years there has been a ______ increase in the cost of living; many families have to depend on the federal aids. A. ponderous B. powerful C. significant D. violent

单选题Very few people understood his lecture, the subject of which was very ______.