The police were asked to keep an eye open for the little boy who had got lost in the square. 警方奉命密切注意在广场走失的小男孩子(的方向)。
Keep a weather eye open for any small faults with your car- if they're not repaired immediately they could cost you a lot of money later. 汽车无论出什么小毛病，你都要留心——如果不立即修理，说不定哪一天会使你花去许多钱的。
