The correct symbol of "therefore" is __________.[ ]
A. ∵
B. ∴
C. <
D. >
答案:B
— I hear the famous singer Xu Song may come to Ningbo next month.
— Really? _______ he comes, my younger sister will be very excited.
A.If
B.Until
C.Unless
D.Before
柴油机调速试验,升降转速时,联合调节器波动不得超过()次。