1. Diurnal: nocturnal::

A. Warm: hot
B. hot: cold
C. Night: day
D. Near: far
Is it b?

I agree.

Diurnal and nocturnal are opposites.

If C were Day: night, that would be correct, but as C is written, they are in the wrong order.

Warm and hot are not opposites.

B and D are opposites, but I think B is the better choice since daytime is usually warmer (sometimes hot!) than nighttime is.