如果關係代詞that在從句中做賓語，就可以省略。如： the flowers （that） I bought yesterday.... that指代flowers，在從句中做bought的賓語，就可以省略。 做主語的話就不能省。如： All that glitters is not gold. 發光的不都是金子。 that在從句中做glitter的主語，所以不能省。
there's nothing I can do about it.
解析：這個句子nothing後面省略了引導詞that，that在句子中引導定語從句，由於that在定語從句中做賓語，所以that可以省略。
Is there anything that you are allergic to?
解析：這句話的that不能省略
當先行詞是anything nothing something everything等
後面的連接詞必須是that且不可以省略.
綜合歸納：賓語從句中that一般情況可省 ，但也並不是任何情況下都可以省略.
賓語從句
1． 定義：用作賓語的從句叫賓語從句.
2． 構成：關聯詞+簡單句
從屬連詞that.如：
He told us that he felt ill.他對我們説他感到不舒服.
I know he has returned.我知道他已經回來了.(that省略)
注:賓語從句中that一般情況可省 ，但that在引導賓語從句時也並不是任何情況下都可以省略.在以下情況下，that不能省略.
1． Everybody could see what happened and that Tom was frightened.(and連接兩個賓語從句，that賓語從句放在and的後面時，that不能省略.)
大家都會看出所發生的事情並知道Tom非常害怕.
2．I know nothing about him except that he is from the south.(that引導的賓語從句作介詞賓語時，that不能省略.)
對他我一無所知，只知道他是南方人.
3．That he ever said such a thing I simply don’t believe.(that從句位於句首時，that不可省略.)
我簡直不相信他曾説過這樣的話.
4． We decided，in view of his special circumstances，that we would admit him for a probationary period.(主句謂語動詞與that從句之間有插入語，that不可省略.)
品位站
