Possible answers:
(1). animals;
(2). epidermal;
(3). Allergies;
(4). negative;
(5). dangerous;
(6). graptolites;
(7). group of atoms;
(8). homogenous;
Given those answer options, answer the question: Fact 1: Antigens are molecules that the immune system recognizes as foreign to the body. Fact 2: Molecules are a group of atoms. Given the two facts above, what type of antigens does the immune system recognize as foreign to the body?
A:
(7).