1.warn sb (not) to do 警告（劝，劝诫，提醒）某人（不）要做某事
特别注意这个结构的被动语态也是经常的考点。
The patient was warned not to eat oily food after the operation.
The doctors warned the patient not to eat oily food after the operation.
医生警告病人手术后不要吃油腻食物。
He warned Billy to keep away from his daughter.
他警告比利离他女儿远点。
Mrs. Blount warned me not to interfere.
布朗特夫人警告我不要插手。
Police are warning the public to be on the alert for suspicious packages.
警方警告公众要警惕可疑包裹。
The police warned them not to go out at night.
警察告诫他们夜间不要出门。
He warned her not to walk home alone.
他告诫她不要独自步行回家。
He warned me not to be late.
他提醒我不要迟到。
'I warned you not to phone me,' he said evenly.
“我告诫过你不要给我打电话。”他平静地说。
People are warned not to eat while driving.
人们被警告开车时不要吃东西。
He had been warned not to tell anyone about it.
曾经叮嘱他不要和任何人讲这事。
The visitors have been warned not to swim in this river for several times.
游客们被多次警告不能在这条河里游泳。
I warned you not to buy the old car.
我劝过你不要买那辆旧汽车。
I was warned not to be late.
我被告之不要迟到。
Residents were warned not to be extravagant with water, in view of the low rainfall this year.
鉴于今年降雨量少，居民被告诫不得浪费用水。
Television broadcasters were warned to exercise caution over depicting scenes of violence.
电视台受到警告，要求对暴力场面的描绘采取谨慎态度。
Motorists were warned to beware of slippery conditions.
驾驶员接到提醒当心道路湿滑。
The official was warned not to strain his power.
那个官员受到警告，不可滥用职权。
He was warned not to go there.
有人警告他不要去那里。
2.warn sb of/against/ahout sth警告(通知)某人注意（提防）某事
Members of congress were warned of possible repercussions if their vote went through.
国会议员被警告如果他们的投票通过可能会带来不良影响。
He warned us against pickpockets.
他提醒我们要提防小偷。
He warned the tourists against pickpockets.
他提醒游客要提防小偷。
Police have warned of possible delays.
警方已经通知可能会廷期。
The guidebook warns against walking alone at night.
这本指南告诫夜间不要单独行走。
It seems only right to warn you of the risk.
似乎应该警告你有风险。
The government has warned of stormy waters ahead.
政府已告诫说，以后的局势将很严峻。
I was warned against the wild dog.
人们告诫我提防那条野狗。
He was warned against the danger ahead.
他被告知前面有危险。
3. warn sb off (sth) （尤指以威胁的方式）叫…离开，告诫…不要靠近；劝…不要做；建议…停止做
The farmer warned us off his land when we tried to camp there.
我们想在那里露营时，农场主警告我们不得靠近他的土地。
The police warned the intruder off.
警察警告闯入者离开。
We were warned off buying the house.
有人劝我们不要购买这所房子。
He pressed for a full investigation, but was warned off.
他迫切要求展开全面调查，但是被叫停。