當且僅當

if and only if

to be / to act as / manage / withstand / when / during / ought / should / match equally / equal / same / obstruct / just at (a time or place) / on the spot / right / just at

at or in the very same... / suitable / adequate / fitting / proper / to replace / to regard as / to think / to pawn / (coll.) to fail (a student)

and / moreover / yet / for the time being / to be about to / both (... and...)

barely / only / merely