Problem Solving (PS) | Re: For any positive integer n, the sum of the first n positive

For any positive integer n, the sum of the first n positive integers equals n(n+1)/2 . If m and n are positive integers and m > n, what is the sum of all the integers between m and n, inclusive?

(A) m(m+1)/2 + n(n+1)/2
(B) m(m+1)/2 - n(n-1)/2
(C) m(m+1)/2 - n(n+1)/2
(D) m(m+1)/2 + n(n-1)/2
(E) m(n+1)/2 - n(m-1)/2