以防 ：In case
造句 ：
他们在窗户上加了窗条以防盗贼进入。
They fitted bars to their windows to stop burglars getting in.
可能下雨--你最好带把伞，以防万一（下起来）。
It may rain you'd better take an umbrella (just) in case (it does).
我已筹备了一笔准备基金以防不测。
I have kept a reserve fund in case of accidents.
我把一切东西都锁在保险箱里以防万一。
I took the precaution of locking everything in the safe.
一、against作“逆着”、“对着”、“顶着”解：1.At this moment our automobile is running against the wind.此刻我们的汽车正在逆风行驶。
2.Heat is produced when work is done against friction.当克服摩擦而作功时，有热产生。（原意为“顶住摩擦作功时……。”）
3.A force is needed to move an object inertia.为使物体克服惯性而运动，就需要一个力。
4.That ship will strike against a rock by using some new-type instruments. 那条船使用新式仪器将不会触礁。
二、against作“反对”、“违反”解：
1.We must fight against imperialism.我们必须和帝国主义斗争。
2.Our workshop has regulation against smoking.我们车间有一条禁烟规定。
3.This explanation is against the natural laws.这种解释是违反自然规律的。
三、against作“靠着”、“位置相对着”解：
1.The picture hangs against the wall.这张画挂在墙上。（原意是：“……靠着墙挂着。”）
2.Against the house there stands a water tower in process of construction.房子对面有一个正在建造中的水塔。
3.Their house is over against the laboratory.他们的房子正在实验室对面。
四、against作“对照”解：
1.She was elected chairman by a majority of 40 votes against 10. 她以四十对十票的多数被选为主席。（句中chairman为主语补语。）
2.As against last year, our grain output has increased 6 per cent.与去年相比，我们的粮食生产增加了百分之六。
3.The factory has produced 95,000 tons of sugar this year, as against the 59,300 tons of last year.这个厂今年生产了95,000吨糖，而去年只生产了59,000吨。
五、against作“以防”、“以备”解：
1.They sore up coal against the winter.他们贮藏煤以备冬用。
2.We should save fuel against the day of battle.我们应该节省燃料以备战时之用。
3.We must guard against disease.我们必须预防疾病。
