a method by which.....

groundkeeper

In the United States, a primary election is a method----- voters select the nominees for public office.

(A)that

(B)is that

(C)by which

(D)by those

answer is C, but why not A ,笨笨地ask........

思愔奶茶

横线前后都是完整句，所以填by which 引导壮语从句

that引导定语从句，从句是不完整句