I'm sure you'll achieve it in the end ________ you keep on doing something．（ ）
A．so thatB．as long asC．unless
What did the teacher say to you？
He asked me______．（ ）
A．why I look unhappy then
B．when did I go home last night
C．how could I solve the problem
D．if I had got everything ready
I still haven't found my pet dog．
I'm sorry to hear that．You______ be very sad．（ ）
A．canB．shouldC．mustD．will
Why did she______your invitation？
Because she had an important meeting to attend that day．（ ）
A．turn downB．put awayC．look upD．hand in
Her father tried to______ that nothing unusual had happened．
In fact，it was not serious．（ ）
A．imagineB．pretendC．meanD．warn
Look，the boss is very angry with Alex．
Well，he came late again．But that's no______ to shout at him．（ ）
A．problemB．lessonC．excuseD．Reason