Qian Xuesen tried many times _________ he found the solution to the puzzle about space technology.
#31596
A
after
B
before
C
since
D
when
推荐题目
A good friend of mine from I was born showed up at my home right before I left for Beijing．
#80680
A
how
B
whom
C
when
D
which
— Whose money is this? — Just leave it it is. It doesn’t belong to us.
#31989
A
even if
B
which
C
where
D
so that
He told me his story in private，__________ nobody else knew what had happened to him．
#30200
A
but
B
so
C
while
D
or
(2014·河南豫北三校高三下学期联考)—May I go and play with Dick this afternoon，Mum?—No，you can’t go out________your work is being done.
#30049
A
before
B
until
C
as
D
the moment