代数式-13a2b3c的数字因数是-13，故单项式的系数是-13．
_______ Japan’s nuclear crisis (核危机) will be solved in 2011 is not known yet.
A．That
B．If
C．Whether
D．What
篮球比赛每次暂停的时间为（）秒钟。
A.20
B.60
C.100
