Unless
Unless (with suppositions) means if not or except that and it is used with negative conditions only.
Example
Future: Unless he buys the tickets for New York this week, we won’t be going.
(If he doesn’t buy the tickets for New York this week, we won’t be going.)
Present: Unless he had a headache, he wouldn’t take an aspirin.
(If he didn’t have a headache, he wouldn’t take an aspirin.)
Past: Unless she had been sick, she wouldn’t have stayed in bed.
(If she hadn’t been sick, she wouldn’t have stayed in bed.)
REMEMBER
IN OPEN-ENDED QUESTIONS, SOME OF YOUR ANSWERS MAY BE CORRECT EVEN THOUGH THE SYSTEM GRADES THEM AS WRONG!
To minimize the chances of being graded incorrectly, mind your orthography, include punctuation marks, such as periods, and use the same contractions, tenses and words as the original example uses.
Let’s review!