Rather than____ on a crowed bus,he aways prefers____ a bicycle.

肯定是D 要么就是prefer to riding或者是prefer riding
至于prefer to为什么+doing,因为prefer to失是连在一起使用,是倾向于的意思,如果to 和 do连在一起使用,那就不用ing形式了
对比一下这个句子Rather than using words,algebra uses symbols to make statements about things.
Rather than____ on a crowed bus,是一个独立结构,一定要用doing 要么就是to do ；B显然不对prefer 不可能直接+do
People prefer to walking several miles to watch the Chinese opera rather than watching TV at home for they can taste the flavor of the spring festival.
再看看这个
总之,无可否认,prefer to do 与 prefer doing to doing 是主要用法,但prefer to doing也是可以；
还有就是Rather than____ on a crowed bus,由于这个逗号使其成为一个独立的句子 所以要用ing形式,这是确实存在的,算是一种书写习惯,还有一种书写习惯就是Rather than____ on a crowed bus,he aways prefers____ a bicycle.句中的两个动词时态保持一致,也就是说由于prefer to 最常用的是+do,所以前面的动词也就用了do
总是.语法比较鸡肋,要多读文章