Choose your answer?

Why do areas in the middle of a large continent generally have more extreme differences in temperature than areas near the coastline?

OPTIONS:
a). There are generally more clouds near the oceans.
b). Landlocked areas are usually at a lower altitude than coastline areas.
c). Coastlines are usually surrounded by mountains that block air masses.
d). Oceans change temperature slowly and regulate the temperature of nearby land.
d).