A block of mass m slides along a frictionless surface with kinetic energy K\textsubscript{i}. It collides with a block of mass 3m that is initially at rest, and the two blocks stick together and slide with total kinetic energy K\textsubscript{f} . What is the ratio K\textsubscript{f} : K\textsubscript{i}？ 
选项为:A:1:1  B:1:2  C:1:3  D:1:4  请回答其中一个选项.