necessaryDo you have the necessary skills for the job?
needDoes she have the skills needed for work of that sort?
mustThe meat must be cooked thoroughly.
essentialClean water is essential for a society's health.
fundamentalSome understanding of grammar is fundamental to learning a language.
indispensableThis book is an indispensable resource for teachers.
be a mustinformalThis book is a must for anyone who loves history.