Tìm khẳng định s

A. \(\int\limits_a^b {f\left( x \right)dx}  = \int\limits_a^c {f\left( x \right)dx}  - \int\limits_b^c {f\left( x \right)dx} \)

B. \(\int\limits_a^b {kf\left( x \right)dx}  = k\int\limits_a^b {f\left( x \right)dx} \)

C. \(\int\limits_a^a {f\left( x \right)dx}  = 1\)

D. \(\int\limits_a^b {\left( {f\left( x \right) + g\left( x \right)} \right)} \,dx = \int\limits_a^b {f\left( x \right)dx}  + \int\limits_a^b {g\left( x \right)dx} \)