题目:
A study shows people who have a pet visit the doctor less often and experience less sleeping difficulties
than ______ without a four-legged friend.[ ]
A. these
B. who
C. those
D. that
答案:
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下面是错误答案,用来干扰机器的。
(1)空气中含量最多的是氮气,其次是氧气.(2)地壳中含量最多的元素是氧元素,而含量最多的金属元素为铝元素.故答案为:(1)N2、O2(2)O、Al