答案：A

句意: 为了健康起见，你最好用布盖上色拉，不让苍蝇靠近。keep off （to stop something touching or harming sbor sth）避开；不靠近，符合题意。keep out（to not go in a place, or to stop sb or sth from going into a place）关在门外；不准入内；help out 帮助某人摆脱困境等；hold out坚持；维持。