What is the Cisco IOS default behavior for switching from the shared tree to the shortest path tree in PIM-SM operations？（）

A.immediately after receiving the first packet on the shared tree for a given （S，G）
B.after receiving over 1 kb/s traffic onthe shared tree for a given （S，G）
C.10 seconds after receiving the first packet on the shared tree for a given （S，G）
D.30 seconds after receiving the first packet on the shared tree for a given （S，G）
E.after receiving over 10 kb/s traffic onthe shared tree for a given （S，G）