来週はテストがあります
There is a test next week, Nは
東京は人が多いです
There are many people in Tokyo、AはBが
どこがいいですか
疑問時(ぎもんじ)+ が. が is used when an interrogative word is the subject, or in a clause in a sentence that is answering an interrogative
毎朝(まいあさ)7時にいえを出(で)ます
Nを、This expresses a place, I leave my house at 7 every morning
友だちといえがに行きました
Nと、This expresses being together with someone. I went to a movie with a friend.