<span>A scientific theory summarizes a hypothesis or group of hypotheses that have been supported with repeated testing.A scientific theory is a well-substantiated
explanation of some aspect of the natural world, based on a body of
facts that have been repeatedly confirmed through observation and
experiment. Such fact-supported theories are not "guesses" but reliable accounts of the real world.</span>
<span>E. Stimulation of T-cell by APC</span>
The initial exposure of the body to an infectious agent e.g. through a vaccine, triggers an immune response most of which rapidly diminishes after the vaccination. However some cells of the immune system called lymphocytes remain with a memory of that pathogen.As a result, if the same pathogen infects a vaccinated person, the memory cells remember and recognize it and rapidly spring into action triggering a much more rapid response specific to that pathogen than the initial exposure, effectively dealing and neutralizing the pathogen.
A is direct variation because the line does not curve and x and y are in a direct ratio