“You were invited to the party,weren't you?”“---,I'd forgott

C.So I was 我确实是
“You were invited to the party,weren't you?”“___,I'd forgotten.”
你被邀请参加这个聚会,不是吗?
确实是,但我忘记了.
考的是so+助动词的用法
如果是 C.So I was 我确实是
是D.So was I 就是我也是
不一样的