he is always studying hard is well known us all.
A. How, to
B. What, to
C. That, to
D. Whether, by
网友回答
A. How, to
B. What, to
(答案→)C. That, to
D. Whether, by
解析：考查主语从句和固定短语。本题第一空的that引导的是主语从句That he is always studying hard, that在句中不充当任何成分，只起引导和连接的作用。第二空是没有固定词组be known to sb为sb所知；句意：他总是认真学习这件事情是我们众所周知的。故C正确。