题目

I do every single bit of housework _______ my husband Bob just does the dishes now and then. A. since    B. whileC. when    D. as 答案：B 解析: while表示对比，意为“而”。我做每一件家务，而我的丈夫Bob只是偶尔做做菜。保持氢气化学性质的最小粒子是（ ）A．H2B．H2OC．HD．H+