Without facts, we can't form a worthwhile opinion for we need to have factual knowledge _____ our thinking. [ ]

A. upon which to base　　　　　　　

B. which to be based on

C. which to base on　　　　　　　

D. to which to be based on

水文（）水准测量要求在每一仪器站前后视距不等差单站不超过3m。

A、二等

B、三等

C、四等

D、五等