Final answer:
Erythema is classified as a Primary lesion, which is the initial skin reaction to an underlying condition causing redness due to capillary dilation and increased blood flow.
Step-by-step explanation:
The level of response of an erythema is A. Primary lesion. Primary lesions are the initial reaction of the skin to an underlying problem or condition, such as inflammation or infection. An erythema is a redness of the skin usually occurring as a result of dilation and increased blood flow to the capillaries, which can be a result of a variety of causes including sunburn, infection, or injury. This contrasts with secondary lesions, which are changes to the skin that occur as a result of the progression or manipulation of a primary lesion.