A hollow sphere is tied to string and the system acts like a simple pendulum . Let the time period of the system be T . By doing which of the following , the time period of the system increases . (Do not consider extension of the string due to mass ) .

Question

$(a)\;By\;filling\;it\;completely\;with\;sand\qquad(b)\;By\;filling\;half\;of\;it\;with\;sand\qquad(c)\;By\;filling\;it\;completely\;with\;water\qquad(d)\;None\;of\;these$