As soon as the white blood cells detect an unknown cell (the pathogen) they produce antibodies or they engulf them, i dont know if this will help but I hope this does :)
Answer:
A. Atmosphere
Explanation:
Atmosphere would be most immediately affected by a decrease in sunlight because sunlight is responsible for the photosynthesis in plants. if sunlight decreases, the photosynthesis reaction is also decreases in plants and less carbondioxide gas is used by the plant from atmosphere for making their food so we can say that atmosphere is greatly affected by the decrease in sunlight.
