sentence2_structure: A(n) organ<>is<>a structure that is composed of one or more types of tissues$$$a structure<>is composed<>of one or more types of tissues
sentence1: One of the simplest essential parts, more commonly called cells , of which animal and vegetable organisms, or their tissues and organs, are composed.
sentence2: A(n) organ is a structure that is composed of one or more types of tissues.
question: What is a structure that is composed of one or more types of tissues?