An exercise on English Tenses

How long ago ......... they leave for Canada?
1. do
2. did
3. does
Have you ever ............ a live cobra?
1. saw
2. seed
3. seen
He .................................... TV when the fire broke out.
1. watching
2. was watching
3. was watched
We .......................................... playing tennis for half an hour when it started to rain.
1. have been
2. had been
3. had
The sky is full of grey clouds. It's ...................................... soon.
1. going to rain
2. will rain
3. has rained
Look at them! They .................................. happily.
1. laughing
2. laugh
3. are laughing
When we arrived at the airport, the aeroplane ...................................
1. had already taken off
2. has already taken off
3. already has taken off
Dad was washing the car while Mum .................................... in the garden.
1. watering the plants
2. was watered the plants
3. was watering the plants
I think they .................................... next Sunday.
1. coming
2. come
3. will come
As I was walking in the park, I ................ a young boy climbing a tall tree.
1. have seen
2. saw
3. had seen