英语:变宾语从句,急急急急急急急急急急..............

是变定语从句吧？如果要是变成定语从句的话，首先要找到先行词，即在两句话当中都出现了的一个名词或代词。 第二句话中的It代替的就是第一句话中的名词Sydney Opera House,所以先行词就是它。最好把第二句话当成主句，第一句话为从句。那么就应该变为：

Sydney Opera House which(that) was a symbol of Australia was used as symbol of the 2000 Olymics.
从which到Australia是从句。把从句去掉后剩下的就是主句。

Sydney Opera House is a symbol of Ausyralia which was uesd as a symbol of the 2000 Olympics.

Sydney Opera House was used as that was a symbol of the 2000 Olympics of Australia