影响水功能区纳污能力的因素有（）

A.水资源质量标准

B.水体稀释自净规律

C.水域的自然背景值

D.排污口的位置和排污方式

It is good practice to use long towlines for ocean tows because the（）.

A.wear on the towline is equalized

B.weight of the towline increases the towing force

C.dip in the towline absorbs shock loads

D.danger of overriding is reduced