If a Homeowner Uses Wood to Heat His House

If a homeowner uses wood to heat his house,

A) he may generate an external benefit if the smoke bothers his neighbours.
B) he may generate an external cost if the smoke bothers his neighbours.
C) the price of the wood represents an external cost to the homeowner,unless he harvests the wood himself.
D) the price of the wood represents an external cost to the homeowner.
E) he may generate an external benefit if the price of heating oil goes down in his region.