Unit 5 The human brain
Grammar: Adverbial clauses ( II )
I. The introduction of if sentences
We use if sentences to talk about possible actions and the results of those actions.
An if sentence has two parts called clauses(从句). Each clause contains a verb.
II. If sentences: actions with definite results (必然发生的动作)
1. If you take a fish out of water, it dies.
2. If you put wood into water, it floats.
3. If you drop a glass, it breaks.
In these if sentences, both verbs are in the same simple present tense（一般现在时）.
III. If sentences: actions with possible results（可能发生的动作）
1. If you study hard, you will catch up with others.
2. We will go out for a picnic if it doesn’t rain tomorrow.
3. I will go to visit him if he comes back tonight.
In these if sentences, the verb tenses are different. The verb in the if clause is in the simple present tense while the verb in the other clause is in the simple future tense.（一般将来时）
unit 5 the human brain 学案.doc