单项选择题

Scientists have spent years into the effects of certain chemicals on the human brain, but with no result（）

A. studying
B. researching
C. investigating
D. inspecting

<上一题目录下一题>

热门试题

单项选择题

The shilpping company will give you a （）of freight if the goods are lost.

A. renewal
B. reminder
C. receipt
D. refund

相关试题