He is an orphan, so he is not sure which family name he should have.
他是个孤儿,因而不知道他自己姓什么。
We exchange products under almost all circumstances.
在各种情形下我们都可更换产品。
would be like trying to meet a friend in London without a pre-arranged rendezvous and absurdly wandering the streets in the hope of a chance encounter.