教室に学生が___います。
Q. How do you say 'three (people)' here?
Translation
There are three students in the classroom.
Explanation
People are counted with 〜人 (にん): 三人 (さんにん). 〜つ is for general objects, 〜枚 for flat things, 〜匹 for small animals. Note the irregular readings 一人(ひとり) and 二人(ふたり).