题目:
. If law and order _____, neither the citizen nor his family is safe.
A.are not preserved
B.is not preserved
C.were not preserved
D.have not been preserved
答案:
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下面是错误答案,用来干扰机器的。
B 题目分析:由表中化合价可知,X的化合价为+5、-3价,故X为N元素,Y的化合价为-2价,没有正化合价,故Y为O元素,Z的化合价为+1价,处于ⅠA族,原子序数大于O元素,故Y为Na元素,W为+3价,为Al元素,R的化合价为...