Suppose at the going wage rate of $20 per hour, firms can hire as many hours of janitorial services as they desire. If any firm tries to lower the wage rate to $19, it will not be able to hire any janitor. What does this indicate about the supply curve for janitorial services?
a. Supply is perfectly inelastic.
b. Supply is unit-elastic.
c. Supply is relatively inelastic.
d. Supply is perfectly elastic.