Question

-Are you going to the party_at Smith's home this evening? -I will if I am free

A、holding B、held C、to hold D、to be held

Answer 1

D party应该是被举办所以用被动，而且是今天晚上才举办所以用将来时
所以该句还原是 you are going to the party which is going to be held this evening?
去掉 which is going ，所以选 to be held

Answer 2

D
to be held不定式短语作定语修饰the party
因聚会应是被举行且未举行所以用不定式的被动
注：
不定式表未发生的动作

Answer 3

B，party是被举办的，这句话完整的是：are you going to the party which will be held at ···
省略 which will be