题干
—Is John doing homework?
—No, he ________ .He is ________a letter.
A：doesn't ,write
B：isn't , writing
C：isn't, writes
D：isn't , writeing
答案(点此获取答案解析）
B
2Z(g)，经12s达到平衡，生成0.6molZ。下列说法正确的是（ ）