卡 ①
进行背景（长镜头）
用 was / were + doing 描写「当时正在延续的背景」，像监控录像在走带。
We were driving home when the strong winds started.
It was raining hard while we were driving back.
While I was waiting at the bus stop, the sky grew darker and darker.
She was reading a novel when the lights in the library suddenly flickered.
The wind was getting stronger while we were walking along the river.
I was watching the road carefully because the rain was beating against the windshield.
卡 ②
一般过去突变（快门）
用 did / 点动词过去式 写「打断、开始、发生」的短事件，像快门咔嚓一下。
While we were playing football, it started to rain heavily.
I was listening to music when my phone suddenly rang.
He was typing an email when the boss knocked on the door.
We were cooking dinner when someone knocked loudly at the gate.
She was jogging in the park when she heard a long, sharp horn.
They were still discussing the plan when the fire alarm went off.
卡 ③
瞬间动词陷阱
find out / come across / realize / hear 等表「察觉、偶遇、听说」时常用一般过去，避免误写成进行时表「结果态」。
When he found out the truth, he stayed calm.
While I was walking in the park, I came across an injured bird.
I didn't notice the warning sign until I came across it near the gate.
She realized she was on the wrong bus when the conductor called the next stop.
We heard a strange noise while we were exploring the old house.
He found out the meeting was canceled when he checked his email that morning.
卡 ④
双线并行（While A…, B was…）
两条同时进行的长动作，用 while 连接，表示在同一时间轴上并行。
While I was doing my homework, my mother was cooking dinner.
While they were sleeping, a thief broke into the house.（教材警示句，仅作悖论教学）
While Dad was repairing the bike, I was holding the flashlight for him.
While the students were writing the test, the teacher was walking around quietly.
While one team was celebrating on the field, the other team was leaving in silence.
While the baby was sleeping, Grandma was knitting beside the window.