“啊”、“吗”、“呢”、“吧” are modal particles.In oral Chinese,you can use them in your customs.But please pay attention to these words "吗”、“呢”、“吧”.If you want to ask yes— or— no questioon,use "吗” instead of "呢“.For example:"你是学生吗？”，you shouldn't say:"你是学生呢？”

If you know he or she is a student,but not be sure,you can say:"你是学生吧？”.Note also that only "啊“ can be used alone in these words.

  They are so easy,right? anything question?