根据语法，骑自行车用by bike 或者 on the bike.这是个定语从句，非限制的定语从句里的引导词前面有介词的很少，所以尽量学定语从句。所以介词用by,所以这几个答案，第一个好

根據您句子的程序，可以這樣說： Bikes are useful. With them, we can travel faster than by foot. Bikes are useful. Using them, we can travel faster than on foot. Bikes are useful. We can travel faster on them than by foot. by foot 比較好一點。 也可以簡單地說： Bikes are useful, they're faster than walking. 這是一種地道的說法。

Since we travel faster on any bike compared to on foot, these sentences are wrong. The third and fourth will only make sense when you are only talking about those bikes which help us to travel faster. Even in that case, the 3rd and 4th sentences should be prefixed with "those". A better way to say this is : Bikes are useful because they enable us to travel faster than on foot Bikes are useful because traveling on them is faster than on foot Traveling on bikes is faster than on foot and as a result, bikes are useful.

I don't think any of these sound right. I believe #4 sounds the best. It should be something more like: Bikes are very useful because we can travel faster on them than on foot / than when we are walking.