An ideal spring - mass system is oscillating . The one which remains some during the entire S.H.M period is

Question

$(a)\;P.E\;of\;the\;spring\qquad(b)\;K.E\;of\;the\;blrk\qquad(c)\;Mechanical\;energy\;of\;the\;system\qquad(d)\;None\;of\;these$