In many countries government reports legal papers and most business letters are the main

问题补充：

In many countries, government reports, legal papers and most business letters are the main situations English is used.

A. that

B. when

C. which

D. where

答案：

A. that

B. when

C. which

(答案→)D. where

解析：考查定语从句。句中先行词为situations，在定语从句中作地点状语，故选D。