certain - adj. not having any doubt about something; convinced or sure
positive - adj. thinking that a good result will happen: hopeful or optimistic
modal verb - a verb (such as can, could, shall, should, ought to, will, or would) that is usually used with another verb to express ideas such as possibility, necessity, and permission
auxiliary verb - a verb (such as have, be, may, do, shall, will, can, or must) that is used with another verb to show the verb's tense, to form a question, etc.
Now it’s your turn. Write a sentence using may, might, or must. We'll check your grammar in the comments section.