预防儿童手足口病的环境消毒液可用“84”消毒液,其主要成分是NaClO ,NaClO中氯元素的化合价为
A:-1
B:+1
C:+3
D:+5
读“水循环示意图”,完成下题.
What colour is it?
函数y=log2x-12x的零点个数是( )
I am sure that he is calm enough ____ this problem.