[单选题]
Two blocks of masses1 z;pff,f gen4eap .))b52x8jjatif e .c v,c9e j: )zblfnlz;$m$ and $2m$ approach each other and collide on a horizontal smooth surface. After the collision, they move together. The speeds of the blocks before the collision are $5v$ and $2v$ as shown.
Which of the following correctly gives the speed of the blocks after the collision and the nature of the collision?
A. Speed after collision is $3v$; Nature of collision is Elastic
B. Speed after collision is $\frac{v}{3}$ ; Nature of collision is Elastic
C. Speed after collision is $3v$; Nature of collision is Inelastic
D. Speed after collision is $\frac{v}{3}$ ; Nature of collision is Inelastic
