SAT question explanation

问题描述:

SAT question explanation
When the phone rang,Bob picked it up,optimistically that it was Sheila calling.
Barron:writing section 上的句子改错.
正确答案是把optimistically改成optimistic.但是我还是不知道原因.
if you have the solution,please let me know asap.ty
如果是省略,什么时候可以辨别

我的理解是这个句子省略了一些东西,可以补完成:it is optimistic that...或者he feels optimistic that...
这样就能看出来要用adj而不是adv了