The variables X, Y, and Z represent polynomials where X = a, Y = 3a – 5, and Z = a^2 + 2. What is X^2Y – Z in simplest form?
a. 2a^2 – 5a – 2
b. 3a^3 – 6a^2 – 2
c. –3a^3 – 2
d. –3a^2 – 2