--Every means has been ______. --No one is effective.

--Every means has been ______.

--No one is effective.

A.tried for

B.tried on

C.tried in

D.tried out

答案及解析： D

解析：

无A、C两项表达法。try on表示“试穿”，而此处表示“试验某物来检验其功能、效果等”，用try out。