Use the Accompanying Figures to Answer the Following Question

Use the accompanying figures to answer the following question.
-The flat line at the left in (b) probably represents _____________.

A) the body's physiological processes coping with low doses of a toxicant
B) competing effects of some other substance whose effect wasn't measured
C) the fact that no toxicant was introduced until the response line begins to rise
D) that no data were collected for the flatline area
E) the fact that there is no physiological effect of the toxicant at low doses