so at 8AM the temperature was less than -7C, so recall that on the negative side, the farther from 0, the smaller, so that number could be say -8C, or -9C or -10C or even say -20C, all those are lesser than -7C, and therefore colder as well.
let's say it was -20C, by noon it went up by 7C, so it became -20 + 7 = -13, well, -13C is still less than -7C, so that'd be true for the B) statement.
let's say it was -10C, by noon it went up by 7C, so it became -10 + 7 = -3, well, -3 is more than -7 and less than 0, so that'd be true for the D) statement.
