If you go to visit London,you will see a lot of buses and cars on the road,you will also see a lot of bikes because more people travel by bike.Why? There are a lot of reasons for this.First,it's very cheap to buy a bike,and riding bikes is quick, too.You often need to wait for a bus for half an hour.When the bus comes,there are so many other buses and cars on the roads so the bus moves very slowly.The underground train is quick but very expensive. I travel to work by bus for about four years.I often arrive at work late and feel tired.Then one day , a friend of mine says, "I go to work by bike,why don't we travel together?""Because my bike's old,"I answer,"and there are so many buses and cars on the road.I feel afraid...""Don't be afraid!"says my friend,"If you follow me and we ride slowly,you will be fine." Two days later I buy a new bike.We go slowly, but we arrive at work quickly. I spend 40 minutes going by bus, but only half an hour by bike! Now I love riding a bike. And I feel healthy. Many people think my idea is good and maybe you'll see more bikes on the road in the future. Many people think in the same way as I do.That's why you see a lot of bikes on the road.Who knows,perhaps in the future we'll have roads for bicycles only.I hope so! Which is NOT mentioned about the good things of riding a bike in the passage? A) we can have more time. B) we don't need to pay much money. C) we can keep healthy. D) we can keep the air clean.
Answer:
D