Assume That the Graph Below Describes the Current Labor Market

Assume that the graph below describes the current labor market for nurses in a mid-sized city and that the labor market is perfectly competitive. Suppose that several years ago the supply of nurses in this city was S₀. What might explain the change from S₀ to S₁?

A) an increase in nurses' wages
B) a decrease in nurses' wages
C) increased immigration of people trained as nurses in other countries.
D) increased employment opportunities outside of nursing.