等质量的CuO和MgO粉末分别溶于相同体积的硝酸中,得到的Cu(NO3)2和Mg(NO3)2溶液的浓度分别为a mol·L—1和 b mol·L—1,则a 与b 的关系为() A.a=b B. a=2b C. 2a=b D. a=5b 答案:C
Take the lift to the eighth floor and turn right.You ________ have any trouble finding my office.
[ ]
A.
needn't
B.
mustn't
C.
don't
D.
shouldn't