制备标准溶液时,必须除去水中的()。
A、Na+;
B、CO2;
C、CL-;
D、O2。
参考答案:B
下列运算正确的是( )
A.(-2)2=4
B.-22=4
C.(-2)3=-6
D.-32=9
. The boy lost his parents in such a terrible earthquake, so he was ______by the government.
A.brought out
B.raised up
C.grown up
D.brought up