2.1 The Present Perfect—Form

COMPREHENSION Based on the reading, write T for true or F for false.

1. Scientists have begun to study risk taking in animals because they are more interesting than humans. 2. Lee Dugatkin has studied risk-taking behavior in birds. 3. Research has shown that teenagers take more risks if they are with friends.

THINK ABOUT IT Discuss the questions with a partner or in a small group.

1. How did you answer the question about swimming toward a bigger island in the first paragraph of the reading? Why did you make this choice? 2. Do you believe that animal research can help explain human behavior? Why or why not?

SUBJECT HAVE/HAS (+ NOT) PAST PARTICIPLE I have taken some risks.

You have not seen We have read the photographs. about risk taking.

Scientists have

studied risk in animals. There have been interesting experiments. He has not researched humans. There has been a new study.

EXPLANATION Use have with the subjects I, you, we, they, or there + a plural subject.

Use has with the subjects he, she, it, or there + a singular subject.

Notes: 1. The contraction for have not is haven’t. The contraction for has not is hasn’t. I haven’t taken a lot of risks in my life. Dugatkin hasn’t studied rats. 2. We can contract the subject pronoun with have or has: I’ve, you’ve, we’ve, they’ve, he’s, she’s, it’s. I’ve read about animal behavior. She’s never taken many risks.

The apostrophe s (’s) can mean has or is. The verb form following the contraction will tell you what the contraction means. He’s studied human behavior. = He has studied human behavior. He’s studying human behavior. = He is studying human behavior. 3. We often contract singular nouns with has, especially when speaking. The researcher’s won many awards. This article’s been downloaded by a lot of students. 4. We can contract there + has. There's been a study of teenage risk taking.

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