A.+→
B.→+
C.+→
D.→+
答案:D
People in some countries waste water______ people in others don’t have enough to drink.
A.while
B.because
C.if
D.so
目前有()类消防产品实行强制性产品认证管理制度。
A、21
B、9
C、15
D、4