There are nice letters in this word.The first letter is“c”.T

There are nice letters in this word.The first letter is“c”.The last one is“m”.And there are two“s”and two“o”in it.We study in it.What is it?
我还有一道题不怎么会。There are three letters in this word.The first letter is“e”.Without it you can’t see.What is it？