12.After his father died,he left his home town.
He left his home town after the【 dead of 】his father.
13.Don’t forget to turn off the gas before you leave the kitchen.
Don’t forget to turn off the gas 【before leaving】the kitchen.
15.She won’t go to see the play because she has lost her ticket.
She won’t go to see the play 【because of】losing her ticket.
16.She went for a walk after she had supper.
She went for a walk 【after supper】.
17.I could swim when I was eight years old.
I could swim 【at the age】 of eight.
18.He was late for school because it rained heavily.
He was late for school 【because of】 the 【heavy】 rain.
19.I don’t know how I can answer the question.
I don’t know 【how to answer】 the question.