by不可以舍去,这里由于提问是how much也就是提高了多少,所以用improve by写成陈述句应该是some cyclists's performance improve by 2% at ...不可以写成some cyclists's performance by impoving然后加个动词原型组成一句话。如果只问是否有提高就是Did some cyclists's performance improve at the 1996 Olympic Games?不用by...
可以省去,但意思不一样了。用by是问百分比,回答应该是...%。省去by,问的是具体提高了多少“分”之类的衡量标准数。可以写成陈述句some cyclists's performance improve by 2%......some cyclists's performance by impoving......对不对取决于前面用什么动词。如:he...