(Many) a problem concerning the agricultural (production) (have been) solved (this way).（　）

A:Many B:production C:have been D:this way

（）more careful, such spelling mistakes might have been avoided.

A:You had been B:You have been C:Had you been D:Have you been

(I have been) told that he (will have come) if he (were) (able).

A:have been B:will have come C:were D:able

These compounds could not have been formed if the chemical reaction ______ stopped.

A:have been B:has been C:had been D:were

These compounds could not have been formed if the chemical reaction ______ stopped.

A:have been B:has been C:had been D:were

(I have been) told that he (will have come) if he (were) (able).

A:have been B:will have come C:were D:able

______more careful, such spelling mistakes might have been avoided.

A:You had been B:You have been C:Had you been D:Have you been