▲问题一：这个从句是什么从句？

在你的句子中，Sherry's already staking her claim on him 到底是什么从句，不同的语法学家有不同的理解，有时同一语法学家在不同的语法著作中也会有不同的分析方法，比如张道真在其《张道真英语语法》上认为：

……有时可用先行词 it 作形式上的宾语，而把宾语从句放到后面去：

I take it you have been out. 我猜你刚出去回来。

Legend has it that Wu Sung is buried at Hangzhou. 传说武松葬在杭州。

Rumour has it that they eloped. 谣传他们私奔了。

而在其《英语语法大全》上则认为：

……在下面句子中that从句是it的同位语：

Rumour has it that the king is ill.

He took it that I had left for London.

He will have it that you have insulted him.

▲问题二：引导同位语从句的 that 可以省略吗？

通常不省略，但这并不绝对，偶尔也可见到省略that的例句。例如：

There was a risk the brain might be starved of oxygen. 大脑可能有缺氧的危险。

又如上面《张道真英语语法》中的第一句也省略了that：

I take it you have been out. 我猜你刚出去回来。