PLEASE HELP ASAP

A specific immune response begins when a white blood cell comes in contact with an antigen (any substance that the immune system does not recognize as part of the body). What external factor typically triggers a specific immune response?

A. an invasion of a microorganism from the external environment
B. a fluctuation of the external air pressure
C. a large release of adrenalin by the endocrine system
D. a change in the external temperature

the electromagnetic energy from the sun arrives in the form of visible and invisible light.

this age may represent the age of the earth's accretion, of core formation, or of the material from which the earth formed. this dating is based on evidence from radiometric age-dating of meteorite material and is consistent with the radiometric ages of the oldest-known terrestrial and lunar samples.

if you look up in the top right corner you'll see your current profile picture, click than click "view profile" you'll be able to change it there.

layer 3 is younger than layer 6.