I cannot forgive myself for not seeing my mother when she was sick in bed.
母亲病的时候我没能去看她,为这件事我永远不能原谅我自己。
When the weather is hot, we turn on the air conditioner.
天热的时候就开空调。
Who could have imagined, in the mid 1970s, for example, that by the end of the 20th century, computers would be as common in people's homes as TV sets?