The cost of 1 unit of electricity during a 4 year period is given below.

Year 1, $1 per unit.

Year 2, $1.5 per unit.

Year 3, $1.2 per unit.

Year 4, $2 per unit.

If a factory spent equal dollars each year for electricity what was the average cost of a unit of electricity during the 4 year period?

A. $ 1.333

B. $1.250

C. $1.425

D. $1.175

E. $1.500