包装箱为何是packing case而不是packed case?

Case Jack packed all the things in a case, 是pencil case,还是pencil-case? have you packed your t yet?yes,i have packed it in my case单词 什么事case by case case by case pecil-case是词组吗 BASKET CASE是啥意思? 是prepare the case还是prepare for the case pencil case 中间需要加横线吗?是pencil-case? switch(a){ case 'a':case 'b':case 'c':输出语句； break； }这是运行的哪一个 in case