假使
In case he comes,let me know.
如果他来的话,告诉我一声.
免得,以防
Be quiet in case you wake the baby.
轻点儿,别吵醒婴儿
也许,说不定
Take your skates in case you decide to go skating.
把溜冰鞋带去,说不定你们要溜冰呢.