As shown in the figure, on a rough horizontal plane, there are two pieces of wood 1 and 2 with mass M1 and M2 respectively. In the middle, they are connected by a light spring with original length L and stiffness coefficient K. the sliding friction coefficient between the block and the ground is μ. Now, a horizontal force is used to pull the block 2 to the right. When the two blocks move at a constant speed, the distance between the two blocks is () A. L+μkm1gB. L+μk（m1+m2）gC. L+μkm2gD. L+μk（m1m2m1+m2）g

As shown in the figure, on a rough horizontal plane, there are two pieces of wood 1 and 2 with mass M1 and M2 respectively. In the middle, they are connected by a light spring with original length L and stiffness coefficient K. the sliding friction coefficient between the block and the ground is μ. Now, a horizontal force is used to pull the block 2 to the right. When the two blocks move at a constant speed, the distance between the two blocks is () A. L+μkm1gB. L+μk（m1+m2）gC. L+μkm2gD. L+μk（m1m2m1+m2）g

Study on block 1. Block 1 is subjected to gravity, spring pull, ground support force and friction force. According to the balance condition, the spring force F = μ m1g & nbsp; & nbsp; and the spring elongation length x = FK = μ m1gk is obtained by Hooke's law. Therefore, the distance between two blocks is s = L + x = L + μ km1g when two blocks move at a uniform speed together. Therefore, select a