题目

在2L容器中发生反应N2＋3H2  2NH3，经一段时间后NH3的物质的量增加了2.4 mol，这段时间内用氢气表示的反应速率为0.6mol /（L·s），则这段时间为A．6s             B．4s              C．3s               D．2 s  答案：C解析: The last time I ______ Jane, she ______ cotton in the field. A. saw; was picking B. saw; picked C. had seen; picked D. had seen; was picking