⏳ 完成式同進行式
揀啱時態可以表達一個動作係已完成、仲進行緊、定係喺另一件過去事之前發生。掌握以下三種形式（have + done、have been + doing、had + done）。
- present perfect — have / has + 過去分詞：過去開始，到而家仍然成立或有關。
- present perfect continuous — have / has been + -ing：一直持續到而家嘅活動，強調做咗幾耐。
- past perfect — had + 過去分詞：更早嘅過去，喺另一件過去事之前。
perfect
I have worked here since 2020.
重點係事實：我 2020 年開始，到而家仲喺度。
continuous
I have been working since 8 a.m.
重點係活動：做咗幾耐（仲睇得出 — 我好攰）。
past perfect
When I arrived, the train had left.
兩件過去事：火車先走，跟住我先到。
睇時間提示同意思，再揀啱形式。
留意助動詞（have / has / had）同由一般現在式嘅轉換。揀出配合時間提示嘅版本。