Your Neighbor Has Just Planted Some Fragrant Flowers

Your neighbor has just planted some fragrant flowers. The wonderful scent drifts into your room and makes you happy.

A) This scent is an internal cost to you.
B) This cannot be an externality since you are enjoying the scent.
C) This is an externality since you get a benefit from your neighbor's flowers.
D) The social cost of this activity is entirely borne by you neighbor.