I walked/was walking in the park when I saw/was seeing a squirrel eating nuts in a tree.

I was walking in the park when I was seeing a squirrel eating nuts in a tree.

I was walking in the park when I saw a squirrel eating nuts in a tree.

My mum ordered/was ordering a pizza while I did/was doing my homework.

My mum was ordering a pizza while I was doing my homework.

My mum ordered a pizza while I was doing my homework.

The rain poured/was pouring down when I realised/was realising I had left my laundry outside.

The rain was pouring down when I was realising I had left my laundry outside.

The rain was pouring down when I realised I had left my laundry outside.

While I talked/was talking on the telephone, the doorbell rang/was ringing.

While I was talking on the telephone, the doorbell rang.

While I talked on the telephone, the doorbell was ringing.

The meeting went/was going really well until a pigeon flew/was flying into the window.

The meeting was going really well until a pigeon was flying into the window.

The meeting was going really well until a pigeon flew into the window.

I needed/was needing to go to the bank but then it started/was starting to rain.

I needed to go to the bank but then it was starting to rain.

I needed to go to the bank but then it started to rain.