✔ 最佳答案
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?