为什么是a lot of exercise而不是a lots of exercises?

In the after-class activities,the students had plenty of______and got a lot of useful __A.exercises,experiencesB.practices,experienceC.practice,experienceD.exercis,experiences答案怎会是C 为什么是a lot of exercise而不是a lots of exercises? This kind of machine___ a lot of noiseA bringsB has C takesD produces为什么是D？ MIss Green spent a lot of money (buy) new clothes 为什么是buying? MIss Green spent a lot of money (buy) new clothes 为什么是buying? MIss Green spent a lot of money (buy) new clothes 为什么是buying? MIss Green spent a lot of money (buy) new clothes 为什么是buying? 为什么是I have a lot of clothes tobe washed而不是to wash A lot of ice cream,hamburgers and cola is not healthy 为什么是is A lot of ice cream,hamburgers and cola is not healthy 为什么是is people coming to the charity show donated a lot of monry,为什么是coming? I take a lot of exercise and am very fit 中的am为什么是对的? Charles Dickens ( wrote ) a lot of novels.内填的为什么是wrote而不是原形? this pair of shoes cost/costs a lot ?this pair of shoes costs a lot ?又为什么是they fit me very well? in order to improve her English,_____a.Jenny'father bought her a lot of tapesb.Jenny bought a lot of tapes for herself为什么是b? I drink a lot of juice every day.改为一般疑问句为什么是Do you drink a lot of juice every day? on each side of the street(grow)a lot of trees 为什么是grow不是are grown Mary always has a lot of work to do为什么是to do 而不是被动式to be done?