1. what does a vaccine contain?\nantibodies\ninfectious particles\nt cells\nantigens

Brief Explanations:

Vaccines work by introducing a substance that triggers the immune system to produce its own antibodies and immune cells. Antigens are molecules that the immune system recognizes as foreign, and vaccines contain either weakened/inactivated pathogens (which have antigens) or isolated antigens to stimulate an immune response. Antibodies are produced by the body in response to the vaccine, not contained in it. Infectious particles would be a harmful active pathogen, which vaccines do not use in an infectious form. T cells are part of the body's immune response, not a component of vaccines.

Answer:

antigens