一般每一次注意起伏周期平均约为（）
A.5-9秒
B.7-9秒
C.8-10秒
D.9-10秒
参考答案：C
I would take the slowest train ____by air. [ ]
A. rather than going
B. rather than go
C. rather than to go
D. rather than to going
试述系谱法的优缺点
