28. Two blocks of mass 1.0 kg and 3.0 kg are connected by a string which has a tension of 2.0 N . A force F acts in the direction shown to the right. Assuming friction is negligible, what is the value of F ?
(A) 2.0 N
(B) 4.0 N
(C) 6.0 N
(D) 8.0 N