A:are using, have added
B:is used, are adding
C:are being used, have been added
D:being used, were added
下列各句中,没有语病的一句是( )
课外探究时,某兴趣小组同学选择了“金属和酸反应快慢与什么因素有关”课题.
已知a是实数,a-i1+i是纯虚数,则a=( )