Evolution is a scientific theory used by biologists. It explains how animals and plants changed over a long time, and how they have come to be the way they are. The Earth has been around for a very long time, about 4.5 billion years. During the first three billion years on Earth, there were only bacteria. Jellyfish were the first species to appear around 700 million years ago.   We know that living things have changed over time because we can see their remains in the rocks. These remains are called ‘fossils’. We know that the animals and plants of today are different from those of long ago. The further we go back the more different the fossils are.   Scientists know evolution has taken place because of the research they have done. Scientists have been collecting evidence for more than 150 years. At the same time, evolutionary questions are still being researched by biologists. The theory of evolution is the basis of modern biology. Nothing in biology makes sense without it. Question 31. The word 'those' in paragraph 2 refers to__________ A. remains B. animals and plants C. fossils D. rocks Question 32. According to the article, what does evolution help to explain? A. how long the earth has been around B. how biologists use scientific theory C. how layers of rock have formed and become the way they are D. how animals and plants changed and become the way they are Question 33. According to the article, what are fossils? A. kinds of plants B. remains of living things C. kinds of animals D. remains of rocks Question 34. According to the article, how do scientists know that evolution took place? A. because nothing makes sense B. because they have conducted research C. because it has been happening for 150 years D. because people are still asking questions about it Question 35. Which of the following is TRUE according to the passage? A. The Earth has existed for nearly 4 thousand billion years B. Jellyfish first appeared around 700 million years ago C. The animals and plants of today are as same as ones in the past D. Bacteria only existed within three billions years