what fun it is後面加什麼

It is 可用於強調句、定語從句、主語從句等多種句型，舉例如下：

It is(was)that句型,It is+被強調成分+that+句子剩餘部分（強調句）：

可以分別用來強調主語、賓語、地點狀語和時間狀語。如：

It was he who(that)read three books in the library yesterday.(強調主語)

是他昨天在圖書館讀了三本書。

It was in the library that he read three books yesterday.(強調地點狀語)

他昨天是在圖書館裏讀了三本書。

It is+名詞+定語從句：

It was the day my grandmother was angry.

那一天我外婆生氣了。

It is +名詞/形容詞+不定式主語：

It做形式主語，句子真正的主語是不定式。

It was a pleasure to draw pictures.

畫畫是一種享受。