A body is moving with variable acceleartion (a) along a straight line. The average acceleration of body in time interval `t_(1)" to "t_(2)` is :-
A. `(a[t_(2)+t_(1)])/(2)`
B. `(a[t_(2)-t_(1)])/(2)`
C. `(underset(t_(1))overset(t_(2))int"a dt")/(t_(2)+t_(1))`
D. `(underset(t_(1))overset(t_(2))int"a dt")/(t_(2)-t_(1))`
