It's duty of every man to work. The life of a lazy man is of no use to himself and to others. If the man is too lazy to work, he will usually become a not useful man. Everyone, when he is young, should learn some useful work.
    But it's not enough for a man to learn some kind of work. He should put his heart and soul (精力) into his work, and not waste his free time. “Work while you work and play while you play” is as good rule for young people as old.
    There is no better to help to diligence than the habit of early rising, and this, just like all other good habits, is most easily formed in youth (青年). There is an English say “Lost time never returns.” This means that everybody must be diligent, and make good use of time. One must study hard when one is young so that one can make great progress, succeed in life and become useful to one's country. So we can say that diligence is the mother of success.

已知直线l:x+y-6=0和圆M:x²+y²-2x-2y-2=0，圆心为M,点A在直线l上，若圆M与直线AC至少有一个公共点C，且$\angle MAC=30°$，则点A的横坐标的取值范围是(    )

一种传染病在人群中流行，必须同时具备三个基本环节，即____、____和____．