Most people on this island are recreational fishers, and _____, fishing forms an actual part of their leisure time. [ ]

A. accidentally

B. purposefully

C. obviously

D. formally

边坡安全系数的定义是：（）

A.抗滑力（或抗滑力矩）与下滑力（或下滑力矩）的比值

B.下滑力（或下滑力矩）与抗滑力（或抗滑力矩）的比值

C.滑体自重与抗滑力的比值

D.抗滑力矩与下滑力的比值