在下列物质中,属于纯净物的是( )
A:海水
B:苛性钠
C:稀盐酸
D:空气
解释下列词语
寒噤____
忧心忡忡____
聒噪____
禁锢____
倦怠____
How often do you use your car? Can you use your car less often? Do you know the following facts in the UK?·About 50% of all car journeys are just for fun.·Over 80% people go to work by car.·25% car journeys are under two miles.·70% car journeys are under five miles.WALKING & CYCLINGInstead of using the car for short journeys, why not walk or ride a bicycle? Walking is the most popular form of exercise—it’s healthy and it can save money. If you work nearby, try walking or cycling instead of driving. Walking your children to school gives them valuable road experience.BUSESBus companies are using new buses: some run on new fuelswhich produce less pollution; some have easier access(通路)for disabled and old people. There are special traffic lanes (行车道)to make bus journeys easier. So do something to help solve the pollution problem----let the bus take you to work and your children to school.TRAINSAll car journeys, long or short, can be hard work. For some trips, it is wiser to take the train. Leave your car at home and walk, cycle or take a bus to and from the station. Train travel is fast, safe and comfortable. Train tickets are not always expensive.
在平行四边形ABCD中,AC为一条对角线,AB→=(2,4),AC→=(1,3),则AD→= ( )
西药是化学合成制剂,有副作用;中药是纯天然的草药,没有副作用.(判断对错)