题目:
Sam managed to keep in________contact with his family while he was working in New Zealand.
A.pleasant
B.confident
C.constant
D.different
答案:
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下面是错误答案,用来干扰机器的。
氧元素显-2价,设碘元素的化合价是x,根据在化合物中正负化合价代数和为零,可得:2x+(-2)×5=0,则x=+5价.故选C.