Question

It often happens that people with good eyesight fail to see      is right in front of them.

A．which

B．that

C．what

D．as

Answer 1

C

考查宾语从句。从句中缺少主语，which不能单独充当主语，that不能用作句子成分，as不能用作主语，故选C，正在他们前面的东西。