麻煩幫忙分析一下這個句子的結構～Why was the origin of life a sample step in

題目：

麻煩幫忙分析一下這個句子的結構～Why was the origin of life a sample step in the Earth's history?

解答：

Why 疑問副詞作狀語
was 謂語
the origin of life主語
a sample step 表語
in the Earth's history 狀語
把句子換成陳述句,成分會更加明了：
The origin of life was a sample step in the Earth's history
再問： 那麻煩問一下這個表語是個什麼用法啊
再答： a sample step 是名詞作表語 a sample step的核心詞是step，a 和 sample都是定語修飾step