`8.` When Margaret opened the door, the phone was ringing.

`9.` He was sitting in the garden when a wasp stung him on the nose.

`10.` While he was running for a bus, he collided with a lamp post.

`11.` Vicky was having a beautiful dream when the alarm clock was ringing.

`12.` When Alex was seeing the question, he knew the answer immediately.

`13.` The train was waiting when we arrived at the train station.

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Để diễn tả sự việc này đang diễn ra mà sự việc khác xen vào trong quá khứ, ta dùng thì quá khứ tiếp diễn. Sự việc nào đang diễn ra chia thì quá khứ tiếp diễn, sự việc nào xen vào chia thì quá khứ đơn

Cấu trúc thì quá khứ tiếp diễn: S+was/were+V_ing+...

Cấu trúc thì quá khứ đơn: S+V2/Ved+...

when M was opening the door the phone rang

he was sitting in the garden when a wasp stung him on the nose

While he was running for a bus, he collided with a lamp post

vicky was having a beautiful dream when the alarm clock rang

When Alex saw the question, he knew the answer immediately.

the train was waiting when we arrived at the station