David didn’t give up ______ he had failed in the experiment four times．
#57729
A
if
B
while
C
though
D
since
推荐题目
--I can’t solve the math problem because it is too difficult. What should I do? -- _________ ask the teacher for help?
#55905
A
How about
B
What about
C
Why don’t you
D
Why not you
_______ you do, don’t miss this exhibition, for it’s so hard for me to get the tickets.
#56127
A
Whatever
B
However
C
If
D
Who
I was just falling asleep ____ there was a loud knock at the door.
#56801
A
while
B
when
C
until
D
as soon as