Injured cells release chemicals that trigger expansion of blood vessels as well as movement of blood and immune system cells into the area. the response is the
a. inflammatory response
b. counter attack
c. fever
d. complement system response

Option A. "inflammatory response"

Explanation:

Inflammation can be defined as a biological response by our immune system which can be triggered by several factors, such as  damaged cells, toxic compounds, and pathogens.

When a pathogen attacks, an inflammatory response takes place, which results in  an increase in blood flow to the infected area. Then the blood vessels in that area expand, and white blood cells releases from those vessels to recover the infected tissue. The white blood cells, also called phagocyte destroy or engulf the bacteria. During inflammatory response, the infected area often becomes swollen, red and painful.

Thus, inflammatory response is the correct option.