Select correct verbs.

If Paula could go back in time, she wouldask Boris to marry her.

If Paula could go back in time, she would ask Boris to marry her.

Could is often used in sentences with unreal conditions: going back in time is impossible.

If Paula could go back in time, she would ask Boris to marry her.

would + simple infinitive is used as the outcome is completely unrealistic.

If Paula could go back in time, she would ask Boris to marry her.

The main clause in the second type conditional is formed by would + simple infinitive, in this case ask