. Sales of CDs have greatly increased since the early 1990s, when people ________ to enjoy the advantages of this new technology. 
#104797
A
begin
B
began
C
have begun
D
had begun
推荐题目
It _______ long before we ______ the result of the experiment.
#103038
A
will not be; will know
B
is; will know
C
will not be; know
D
is; know
Hurry up, kids! The school bus _______ for us!
#100583
A
waits
B
was waiting
C
waited
D
is waiting
--- I’m sure Andrew will win the first prize in the final.  --- I think so.  He _____ for it for months. 
#103307
A
is preparing
B
was preparing
C
had been preparing
D
has been preparing