A. superb B. superior C. senior D. super

【题目】You won't find it difficult ______ you have mastered it.
A.before
B.while
C.once
D.though

【题目】______ the sun rises, all the stars in the sky disappear.
A.The moment
B.Before
C.Till
D.For

【题目】It is nearly 50 years ______ the People's Republic of China was founded.
A.after
B.before
C.when
D.since

—Well，it’s not surprising. So many people all the time recently.

A. come B. have come C. have been coming D. came

【题目】We'll build a power station ______ water resources are plentiful.
A.where
B.in which
C.which
D.that