I find that listening to English tapes is very useful.
I find _it very_ useful _to_ listen to English tapes.
注:
(a)"very useful" 必须保留.
(b)"find it"; 不必 "find it's ..."
例:
(i) "I find this wine a little sour."
(ii)"I find (it) a little sour"
(不是"find it's a little sour".)