Why was coal preferred to wood as a basic source of energy

A．People found it harder to get a job.
B．People had to live near a source of energy.
C．A lot of wood was shipped to faraway places.
D．Industry developed and people' s living standard went up.

A．Because wood was safer than coal.
B．Because wood burned longer than coal.
C．Because there was more wood than coal.
D．Because they used wood as primary source energy.