More wild tigers have been seen in the forest around this area there used to be very few

问题补充：

More wild tigers have been seen in the forest around this area, there used to be very few.

A. when

B. where

C. what

D. which

答案：

A. when

(答案→)B. where

C. what

D. which

解析：定语从句缺少地点状语in the forest，所以其关系词必须是where或in which.

答案A在定语从句中做时间状语； C what不能引导定语从句； D的which只能直接代替先行词the forest，但是它不能在该定语从句中直接充当成分。