Why Is Mercury Difficult to Observe from Earth

Why is Mercury difficult to observe from Earth?

A) Mercury remains close to the Sun in its orbit and is seen in a dark sky only at sunrise or sunset, close to the horizon.
B) Mercury orbits the Sun very rapidly and moves across our sky very quickly.
C) The orbit of Mercury is very elliptical and tilted at a large angle to the ecliptic, and any position on this orbit is visible only at midnight when Mercury is low in the sky.
D) Mercury is a very small object that orbits a long way from the Sun, thereby reflecting little light back to Earth.