Every means ____ tried out but never with success, as far as my knowledge goes.
C
【句意】就我所知，每种方法都试过了，但都没有成功。
【难点】means虽以s结尾却是单数形式，因此谓语动词应选用第三人称单数。
---Wouldyouliketogooutforawalkwithus?
---_____,butImustfinishmyhomeworkfirst.
The____ofAIDShasledtoanexpansioninresearchseekingacure.