You must do this exercise UNTIL you memorise all these words. You must do this exercise UNLESS you already know these words. Got it? :)

Unless = conjunction 1. except under the circumstances that: I'll be there at nine, unless the train is late. –preposition 2. except; but; save: Nothing will come of it, unless disaster. Until = –conjunction 1. up to the time that or when; till: He read until his guests arrived. 2. before (usually used in negative constructions): They did not come until the meeting was half over. –preposition 3. onward to or till (a specified time or occurrence): She worked until 6 p.m. 4. before (usually used in negative constructions): He did not go until night.

unless= if not until= to; up to; till; before; -- used of time

unless The club is for members only. you can not go in unless you are a member. This means: You can not go in except if you are a member or you can go in only if you are a member. Unless: except if. Until (or till) we until (or till) use to say how long a situation continues: Shall we go now? No,lets wait untill (till) it stops raining. I could not get up this morning.I stayed in bed untill half past ten.