Question

Only when _______ 30 years old ______ to learn English

1. A.
   was he; did he begin
2. B.
   he was; he began
3. C.
   he was; did he begin
4. D.
   was he; he began

Answer 1

C
考查部分倒装。Only+时间状语从句，放在句首时，后面主句要部分倒装，而从句不倒装。所以选C。