The greatest surface area for gas exchange is found in the Alveoli
The Epiglottis prevents food from entering your lungs.
Hope this helped you! c:
Answer:
Lead in 
g of blood 
grams
Explanation:
Given -
Amount of lead in human blood - 
parts per million (ppm)
This is equivalent to g of lead for each million grams of blood
Numerically, it can be represented as -
Lead in g of blood
grams
Lead in g of blood grams
Through my research I found matching questions with similar answers:
A) macrophages
B) antigens
C) antibodies
D) lymph
The best answer to fill in the blank would be the third option C) Antibodies which in the name anti means against, so since the word anti is the same as against, its a battle between antibodies and invaders, so that's why its C).
