What worng in the sentence.

What is wrong in this sentence? 這視乎你想説甚麼...

正解1: I knocked on the door before I entered. 没有特別的意義, 就是字面的意思.

正解2: I had knocked on the door before I entered. 文法上的完整. knock這個動作比entered先完成, 已經完成的動作用過去完成式.

正解3: 你的原句並無錯處^^ 假若有人這様提出問題的話 : What were you doing before you entered?

1. Tense 有問題. 從句子意思看來, 是兩個動作在過去前後完成, 前動作要用 past prefect tense, 後動作用simple past tense.

2. 要簡化句子結構, 在這句不需要用“on” (preposition).

I had knocked the door before I entered.

I was knocking on the door before I entered --> 'was knocking' is wrong
(I THINK) Should be:
I knocked on the door before I entered.