A block of mass m is connected to another .block of mass M by a massless spring of spring constant k. A constant force f starts action as shown in figure, then:

Options

A. as observed from ground both blocks ,will come to momentarily rest simultaneously
B. as observed from their centre of mass blocks will come to momentarily rest simultaneously
C. maximum extension in spring will `(2mf)/(k(m+M)`
D. maximum extension in spring will `(mf)/(k(m+M))`