题干
Try to spend your time just on the things you find _________.
A：worth doing them
B：worth being done
C：them worth doing
D：worth doing
答案(点此获取答案解析）
D
A：worth doing them
B：worth being done
C：them worth doing
D：worth doing
C(g)，若反应物的浓度从2mol/L降到0.8mol/L需20s，那么反应物浓度由0.8mol/L降到0.2mol/L所需的反应时间为（ ）