Which of these types of stone structures is a part of Stonehenge in England?

A Trilithon
B Dolmen
C Cairn

Stonehenge is a megalithic structure that is comprised of an outer ring made of standing stones, topped with horizontal stones and a ring of smaller stones inside. Within this ring are trilithons, individual structures made of two vertical blocks covered with a horizontal one.

The correct answer is Trilithon.