Mark the letter A, B, C, or D to indicate the sentence that best combines each pair of sentences in the following questions. My brother is not old enough. He can't take the driving test.

If only my brother were enough young to take the driving test.

If my brother had been old enough, he could have taken the driving test.

Provided that my brother is old enough, he can take the driving test.

If my brother were old enough, he could take the driving test.