Find examples of Present Simple, Present Perfect and Past Simple of the verbs in the text.

Example: has – Present Simple.

What is evolution?

“Evolution” really has two different meanings to biologists. The term can refer to either as a process or an organizing principle, that is, a theory. Generally, the word evolution means change, and the process of biological evolution is derived from this definition. That is, biological evolution is a change in the features of individuals in a biological population that occurs in the course of generations.

For example, consider the species of organism commonly known as head lice. A species (Latin, meaning “kind”) consists of a group of individuals that can regularly breed together and is generally distinct from other species in appearance or behavior. Most species are physically subdivided into smaller groups, populations, that are somewhat independent of other, populations – that is, most individuals in a population breed with other individuals in the same population. As some parents of small children have discovered some populations of head lice in the United States have become immune to the pesticide permethrin, found in over-the-counter delousing shampoos. Initially, lice infections were readily controlled through treatment with these products; however, over time, populations of lice changed to become less susceptible to the effects of these chemicals. The evolution of resistance can occur rapidly – a study in Israel demonstrated that population of head lice were four times less susceptible to permethrin only 30 months(40 lice generations) after it came into widespread use in that country.

Note that in this example, individual head lice did not “evolve” or change; each individual louse is either susceptible to, or resistant to permethrin. Instead the population in a whole changed from one in which most lice were susceptible to one in which most lice were resistant to the pesticide. This change in the characteristics of the population took many generations. According to the definition above, the lice have evolved.

Change the tense of the predicate on the left in accordance with the adverbial modifier on the right.

1. I am interested in research work. Always

2. I take part in the work of the students’ scientific society. When I was a

student

3 I write my thesis. Now

4 I collected bibliography. Already

5 I take part in the international conference. Next week

6 They’ll finish the article. By the time

you came in

7 I have already passed my candidate exams. Last month

8 I am not good at French. A year ago