back up的意思及造句？

1. (使)后退；倒退回去；倒(车)：例句: He backed up to the loading platform.他(把车)倒退到装货平台。2. (使)倒着上：例句: If you can't drive up the hill forwards, you'll have to back the car up.假如你不能把轿车正着开上山，就只好倒着开上去。3. 支持；援助；为…撑腰...