we must pick up all the litter --------- the campsite after

we must pick up all the litter on the campsite after the barbecue.
我们得把烧烤後留下的垃圾从营地上全部收拾走.
（at用在说营地处有什麼叙述者基本不在营地内,人已经在营地裏活动,指所在地周围存在什麼用on）
you should wash silk clothes with hand
丝质衣服要用手洗.
everything in the school library is put in good order
学校图书馆所有东西被整理的井井有条.
we are busy with a quiz for the festival
我们为做一个节日的考查绞尽脑汁.
busy with意思是“忙於”