[mr.ahmedabdelwahed]

المشاركة الأصلية كتبت بواسطة MAZEN gamal

هناك جملة اخرى وقفت عندها فى unit 4
If only one bird pulled a string;the box didn't move
why he didn't say (wouldn't move
why he used past simple in both sentences
and the sentence which followed is the same
If the two birds pulled a string it moved
I think there is also a mistake as I think he should say the string instead of a string
as it was mentioned before when he said (they had to pull a piece of string) ?????????????????

first of all, you are asking about two clauses, not sentences. When you have a complex sentence with a conditional in one clause, it is not necessary to use a modal verb in the result clause. Both wouldn’t move and did not move are correct here.

In your second question, you are misquoting the book. The book says “they had to pull pieces of string attached to the box. If only one bird pulled a string…” The indefinite article is correct here because the bird pulled only one of the strings. The book continues: “However, if both birds pulled the strings at the same time…” The book is correct. As you say, the definite article should be used because the string has already been mentioned.

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