例句：

　　1. He spends his spare time visiting schools to warn pupils off drugs.

　　他用自己的業(yè)余時(shí)間訪(fǎng)問(wèn)學(xué)校，告誡小學(xué)生遠離毒品。

　　2. Signs across the entrances warn all visitors to stub out their cigarettes.

　　入口處的告示牌提醒游客們熄滅香煙。

　　3.I must warn you against raising your hopes.

　　我必須警告你不要期望過(guò)高。