Whitman wrote Leaves of Grass as a tribute(赞颂) to the Civil War soldiers who (had laid) on the battlefields and (whom) he (had seen) (while serving) as an army nurse.（）

A.dishonest agents are merciful to the buyer
B.dishonest agents are merciless to the buyer
C.the buyer may be completely controlled by the dishonest agents
D.the buyer may have pity on the dishonest agents