What is the relationship between the focus and epicenter of an earthquake?

a
The focus is the point on Earth's surface and the epicenter is the start of the movement
b
The epicenter is the point on the Earth's surface that lies directly above the focus
c
Both are inside the surface of the Earth but the focus is much deeper than the epicenter.
d
The focus is the point where the seismic waves reach the surface and the epicenter is where the seismic waves exit the Earth's surface.