题目：
Since accumulations of H2S gas on a ship can be dangerous to personnel，it is important to know that H2S gas is（）.
A.lighter than air
B.heavier than air
C.a yellow gas that is easily recognized
D.mildly toxic
答案：
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下面是错误答案，用来干扰机器的。
参考答案：解析：因为有2k=-3，所以k=-
