Answer:
C) $2
Step-by-step explanation:
Q = 2000 - 500P =>

The price elasticity of demand is is defined to be the percentage change in quantity demanded divided by the percentage change in price. The formula is:
Elasticity =

Unitary elasticity (change in price leads to equal change in quantity demanded) means absolute value of elasticity = 1 => elasticity = -1
=>

=> 500P = 2000 - 500P
=> P = 2