瓶子装水，吹气和敲打发出的音调怎么区别？

中国资产阶级革命派在近代化探索过程中的突出成就是（    ）

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 & CYCLING

Instead 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.
BUSES

Bus 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.
TRAINS

All 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.

 阅读某初中校园网论坛的帖子，回答问题。

下列哪项措施有利于优生？（    ）