Question

Not until you try to build a machine that does the same task as people do ________．

1. A.
   you realize how is it incredibly hard
2. B.
   do you realize how incredibly hard it is
3. C.
   you realize how incredibly hard is it
4. D.
   do you realize how it is incredibly hard

Answer 1

B
not…until…“直到……才……”。not until如果放在句首，句子结构要倒装。在宾语从句中how修饰incredibly hard，故答案选B项。