Moments determine function

1. A.$\int$₋${}_1^{1}f(x)x^n$ dx = 0 for all n ≥ 0.
2. B.$\int$₋${}_1^{1}f(x)p(x)$ dx = 0 for all real polynomials p(x).
3. C.$\int$₋${}_1^{1}f(x)x^n$ dx = 0 for all n ≥ 0 odd.
4. D.$\int$₋${}_1^{1}f(x)x^n$ dx = 0 for all n ≥ 0 even.

The trap it tests

Hypothesis dropped

A theorem applied without checking one of its preconditions.