Answer: 1) very important. 2) change the idea 3) should, must 4) and have to 6) However 7) abilities 8) ask for permission 10) make a suggestion 11) obligations. 12) impossibility 13) give permission 14) prohibition 15) crucial since they work as helping verbs.
Explanation: Modal verbs are "auxiliaries" that help the verb by changing its meaning. We use them when we want to talk about things in the present or the past. They show possibilities, obligations, abilities, permissions, and prohibitions. Therefore, they are essential for the meaning to change in sentences.
