Answer:
C
Explanation:
To send signals to the blood vessels to constrict or dilate , to increase or decrease blood flow respectively.
Rainwater picks up carbon dioxide from the air and as it percolates through the soil, which turns into a weak acid. This slowly dissolves out the limestone along the joints, bedding planes and fractures, some of which become enlarged enough to form caves.
There’s actually 100 but only 8 of them infect humans