Consider a Firm That Places Coin-Operated Coffee Machines in University

Consider a firm that places coin-operated coffee machines in university buildings.On January 1,2015 the firm has 1500 machines in operation,and on January 1,2016 the firm has 2250 machines in operation.A possible explanation is that
1) there was an increase in productivity of coin-operated coffee machines that reduced the cost per cup of coffee produced;
2) an increase in demand for coffee led to an increase in the price per cup;
3) there was an increase in interest rates.

A) 1 only
B) 2 only
C) 3 only
D) 1 or 2
E) 2 or 3