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?

A2a^2 – 5a – 2
B3a^3 – 6a^2 – 2
C–3a^3 – 2
D–3a^2 – 2