今年の冬は去年___寒くないです。
Q. Which particle completes 'not as cold as last year'?
Translation
This winter is not as cold as last year.
Explanation
To say 'not as cold as last year,' use the comparison standard + ほど + negative: 去年ほど寒くない. より can also occur with a negative predicate, but it produces a different comparison rather than this 'not as ... as' pattern.