单选题 . 
    Charles Darwin is famed for the theory of evolution, which was published in the work On the Origin of Species in 1859. A large portion of the theory developed during an exploratory ocean voyage Darwin made aboard the British Royal Navy vessel HMS Beagle from 1831 to 1836. During that long trip, Darwin had the opportunity to observe plant and animal life in a wide variety of ecosystems, and that led him to conclude that many species slowly evolved into their present forms due to the necessity of surviving in their environments. After returning home, Darwin spent the next couple of decades analyzing and refining his ideas before making them public in 1859.
    The Beagle was a ten-gun naval sloop—a small ship by the standards of the day—and was equipped for long exploratory expeditions with its goal being to survey the coastal waters of foreign lands. The ship made its first such voyage from 1826 to 1830, where it mostly conducted a hydrographic survey of the coastal waters of South America. For its second voyage, the Beagle was to continue its survey work. However, Captain Robert Fitzroy wanted a geologist onboard to examine the land since none had been present on the first voyage, so Darwin was eventually contacted to carry out those duties.
    Setting sail from England in December 1831, the Beagle's extensive voyage took it to the Atlantic and Pacific coasts of Central America, South America, the Galapagos Islands, Tahiti, Australia, New Zealand, and Mauritius before the ship returned to England in October 1836. During the trip, Darwin frequently went ashore to examine the local geology, flora, and fauna, and he collected numerous samples and made extensive notes about everything he discovered. Gradually, as the voyage continued, his observations led him to his pioneering notion about how plants and animals arrived at their present states. After returning home, Darwin published his diary of the expedition in 1839. Known today as The Voyage of the Beagle, the book was well received in its time and went through several printings.
    Large portions of the diary served as the basis for Darwin's later writings, including his work on evolution. Included in the diary were many of Darwin's observations that contributed to scientific studies. For example, Darwin noted that in many places, beds of fossilized seashells had been found at high elevations, which indicated that the land had undergone a tremendous transformation at some time in the past. Darwin also observed that coral atolls formed when volcanic islands sank, leaving behind coral reefs. But his greatest find was the discrepancy in plant and animal life in places that were short distances apart from one another. For instance, the flora and fauna of the Atlantic and Pacific coasts of Panama differed a large amount despite being relatively close to each other. He further recorded the fact that the various islands of the Galapagos had similar plants and animals but that they had evolved with slight differences that helped them survive on the particular island on which they dwelled. The most famous example of this observation is the finches Darwin noticed as having different-shaped beaks, each of which was suited for the main food source on its particular island.
    In the years following the voyage of the Beagle, Darwin contemplated his findings and gradually articulated his famous theory. Nevertheless, he felt unready to publish his work because he wanted to work on other projects to gather more evidence. Then, in the 1850s, he learned that his ideas were similar to those of another naturalist, Alfred Wallace, who had been working in Southeast Asia for years and had come to nearly identical conclusions with Darwin. Once they made contact, in 1858, the two men collaborated on a paper discussing evolution, making it the first published mentioning of the theory. Then, fearful that Wallace would publish a book on the subject first, Darwin's friends urged him to put his work into print. The result was On the Origin of Species in 1859. To his credit, Wallace never felt slighted and publicly supported Darwin and his work when both came under attack. As for the Beagle, it made a third trip similar to the first two and then spent time serving as a guard ship in England's coastal waters.
    *Glossary
    sloop: a sailing ship that has a single mast
    hydrographic: relating to the science of measuring and mapping the surface of the Earth's waters, mostly for the purpose of navigation
    atoll: a coral reef in the shape of a ring that has an enclosed or nearly enclosed lagoon14. 
    Charles Darwin is famed for the theory of evolution, which was published in the work On the Origin of Species in 1859. A large portion of the theory developed during an exploratory ocean voyage Darwin made aboard the British Royal Navy vessel HMS Beagle from 1831 to 1836. During that long trip, Darwin had the opportunity to observe plant and animal life in a wide variety of ecosystems, and that led him to conclude that many species slowly evolved into their present forms due to the necessity of surviving in their environments. After returning home, Darwin spent the next couple of decades analyzing and refining his ideas before making them public in 1859.
    Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect answer choices change the meaning in important ways or leave out essential information.
    During that long trip, Darwin had the opportunity to observe plant and animal life in a wide variety of ecosystems, and that led him to conclude that many species slowly evolved into their present forms due to the necessity of surviving in their environments. ______