. In our class, when the bell rang and the teacher closed his book, it was a ______for everyone to stand up.
#6715
A
mark
B
chance
C
signal
D
measure
推荐题目
Having a fever is the ______________ of SARS.
#6348
A
migraine
B
symptom
C
pneumonia
D
prescription
This chemical works _____.
#7336
A
is rebuilding
B
is being rebuilt
C
are being rebuilt
D
is being rebuilt