He should not have swum in the lake alone .

他本不应该独自一人在湖里游泳的。

They haven 't swum across the river yet .

他们没有游过河。

Have you ever swum in a river ?

你在小河里游过泳吗？

He had swum and boated with them .

他曾和他们一道游泳、划船。

However , someone has swum across the atlantic ocean , but it was assisted .

但是，的确有人横渡了大西洋，但他是在有帮助的情况下完成的。