(a) food web

(b) ecological pyramid

(c) ecosystem

(d) food chain

Correct option – ( a )

Explanation for correct option – food web is composed of organisms of higher trophic level which eat several types of organisms which belong to lower trophic levels .

Explanation for incorrect option – flow of food energy through organisms is called as food chain . All living organisms and non living substances make up the ecosystem . Relationship between different living organisms at different trophic levels is known as ecological pyramid .

Hence correct option is food web