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C, To introduce the main topic.D. To provide background information.26. What did D'Amico do for the sea lion?A.Shehelpedhimgo intothewater.B. She took care of him in theHeadlandsC. She called the Marine Mammal Center.D. She transferred him to the animal center.27.Which of the following is the suitable title for the text?A.A StrangeIslandB. The Rescue of a Sea LionC. Lidia D'Amico's Adventure D. The Struggling Life of MammalsCAn international team of researchers led by the University of Bristol has cast light on Earth'searliest ecosystem， showing that within a few hundred million years of planetary formation,life onEarth was alreadybooming（繁荣的）.Everything alivetodayoriginatesfrom acommon ancestor known as LUCA （Last Universal Common Ancestor）.LUCA is the assumptive common ancestor from which all modern cellular life， fromsingle-celledorganismslikebacteriatothehugeredwoodtreesaswellasushumansoriginates. LUCA stands for the source of the tree of life before it splits into the groupsrecognized today: Bacteria， Archaea and Eukarya.The team compared all the genes（基因） in the genomes of living species，counting thevariations that have occurredwithin their orders over time since they shared an ancestor inLUCA. The time of separation of some species is known from the fossil （化石） record andso the team used a genetic equivalent of the familiar equation used to calculate speed in physicsto work out when LUCA existed, arriving at the answer of 4. 2 billion years ago， about fourhundred million years after the formation of Earth and our solar system.Next， the team worked out the biology of LUCA by modelling the physiologicalcharacteristics of living species back through the genealogy（宗谱） of life to LUCA． Leadauthor， Dr Edmund Moody explained， “The evolutionary history of genes is complicated bytheir exchangebetween lineages（细胞系）：We have to use complex evolutionary modelstoharmonize the evolutionary history of genes with the genealogy of species.Co-author Professor Philip Donoghue said， “Our work reveals insights into early Earth andlife that could not be achieved by any one subject alone. It also demonstrates just how quicklyan ecosystem was established on early Earth. This suggests that life may be booming on Earth-like biospheres elsewhere in the universe."28. What can be learned about LUCA from the text?A. It represents the root of the tree of lifeB. It is only the ancestor of redwood trees.C. It was divided into two groups.D. It didn't change much over time.29. When did LUCA exist according to the text?A. About 4. 6 billion years ago.B. About 3. 8 billion years ago.C. About 4. 2 billion years ago.D. About 400 million years ago.30. What can we conclude from the text?A. LUCA was the only form of life on Earth then.B. LUCA was probably a very complex organism.C. The study of LUCA is the final step in exploring the universe.D. The formation of Earth was closely related to that of other planets.31. What did Philip Donoghue say about their study?A. It was time-consuming.B. It was disappointing.C. It was labor-saving.D. It was meaningful.