JEE Math Practice Question

Let f and g be continuous functions on [0, a] such that f(x) = f(a – x) and g(x) + g(a – x) = 4, then $$\int\limits_0^a \, $$f(x) g(x) dx is equal to :

1. A.4$$\int\limits_0^a \, $$f(x)dx
2. B.$$-$$ 3$$\int\limits_0^a \, $$f(x)dx
3. C.$$\int\limits_0^a \, $$f(x)dx
4. D.2$$\int\limits_0^a \, $$f(x)dx