饮水的适宜氟浓度应控制在
A.0.5mg/L以下
B.1mg/L以下
C.0.5~0.6mg/L
D.0.5~0.7mg/L
E.0.7~1mg/L
参考答案:B
______ Kitty ______ Cathy is going with you because one of them must stay at home.
A.Not only; but also
B.Neither; nor
C.Both; and
D.Either; or
若a为int类型,且其值为3,则执行完表达式a+=a-=a*a后,a的值是______。
A.-3 B.9 C.-12 D.6