multiple choice

[Max_Hinton123]

Researchers speculate that if the birds ______ to evolve in this way, they could eventually become a distinct species.
A) continued B) continue C) will continue D) continues
I've chosen A) but it's wrong , The right answer is B). Why?

 

[Thomas Tompion]

It's a type I conditional (present in the if-clause, future in the main clause).

B and D are present tense, but the subject is plural, so B is the answer.

 

[Max_Hinton123]

It's a type I conditional (present in the if-clause, future in the main clause).

B and D are present tense, but the subject is plural, so B is the answer.

As I know it must be 'will' instead of 'could' in the second part of the sentence in order to be a type 1 conditional.

 

[e2efour]

Not so. Could (or other modals such as might) is used here to comment on the certainty of the result.
If you go out without an umbrella, you could get wet.
If you wrote will, you would be saying that the result (getting wet) would certainly occur.

 

[Thomas Tompion]

Exactly. Could can be many tenses, including the future.