Northern switzerland has a fairly cold climate caused by sea winds from the atlantic ocean, but southern switzerland tends to be much warmer and sunnier. what could cause this difference?

a) cool winds cannot blow across a large lake into the south.
b) switzerland has experienced a drastic climate change in the past few years.
c) the south is at a much higher elevation, so it is closer to the sun.
d) mountains prevent cold air from blowing over into the south.