The correct option is D a<x1<b
According to the Lagrange's Mean Value Theorem, if f(x) is defined on [a, b] such that
(i) it is continuous on [a, b]
(ii) it is differentiable on (a, b)
Then, there exists a real number x1∈(a, b) such that f'(x1)=f(b)−f(a)b−a.