(a) all living organisms

(b) non-living objects

(c) both living organisms and non-living objects

(d) sometimes living organisms and sometimes non-living objects

Correct option – ( c )

Explanation for correct option – an ecosystem consists of living organisms as well as non living objects and their interaction with each other

Explanation for incorrect option – living organisms and non living objects together constitutes the ecosystem . It cant be framed by either one of them

Hence correct option is both living organisms and non-living objects