Question

Henry must have stayed up last night, ________ he looks so tired and sleepy

1. A.
   for
2. B.
   as
3. C.
   though
4. D.
   since

Answer 1

A
考察連詞。A.因為  B.因為；隨著 C. 盡管   D. 因為；既然。for表示所說的理由是一種補充說明, since和as是從屬連詞，說明的是已為人們所知和理由。句意：亨利昨晚肯定熬夜了。因為他看起來如此累和困乏。結(jié)合語境可知選A。