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, 2007 the firm has 1500 machines in operation, and on January 1, 2008 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) 2 only
B) 3 only
C) 2 or 3
D) 1 only
E) 1 or 2