根据文意，补全所缺单词，词首字母已给出。
Overhead bridges can be seen in many parts of Singapore，in the places where traffic is very h _____ and crossing the road is not safe．
These bridges can help people cross roads s _____ ．Overhead bridges are used in very much the same way as zebra crossings（斑马线）．
They are more efficient（效率高的），t _____ less convenient（方便的）because people have to climb up a lot of steps．This is inconvenient to the old．When people u _____ an overhead bridge，they do not hold up（阻挡） traffic．But when they cross a busy road using a zebra crossing，traffic is held up．This is w _____ the government（政府）has built many overhead bridges to help people and k _____ traffic moving at the same time．
The government of Singapore has s _____ a lot of money building these bridges．For their own safety，people should be advised to use them instead of rushing across the road．Old people may find it a little d _____ climbing up and down the steps，but it is still much safer than walking across the road w _____ all the moving traffic．
Overhead bridges are very useful．People， both old and young，should always use them． This will stop accidents from h _____ ．
Key:
1．heavy
2．safely（作状语应用副词形式）
3．though（此处表让步关系，意为“虽然”）
4．use
5．why（此处表达“这就是……的原因）
6．keep
7．spent（spend time ／money in ／on doing sth．意为“花时间／金钱做某事”，其中in常省略）
8．difficult
9．with
10．happening（stop．．．from doing）意为“阻止／防止……去做某事”）
