不可或缺

Function word; no; not; un-; negative prefix; used to form questions or emphasize a statement; sometimes used for rhythm.

Able to; can; may; to permit; to approve; suitable; worth; but; however; certainly; very.

Perhaps; maybe; possibly; or; either; else; sometimes used as a pronoun meaning 'someone' or 'something', or to ask 'who?'

to lack; deficiency; shortage; a gap or opening; a vacant position; imperfect