Critical Thinking: A child appears healthy until approximately 9 months of age. Then the child develops severe
bacterial infections. One after another. Fortunately, the infections are successfully treated with
antibiotics. When infected with measles and other viral disease, the child recovers without
difficulty.

this is because the child's immunity system has improved and the child's immune system can fight all the know bacterias that were given through the antibiotics...

there are no mutiple choices here

relationship between pressure and air volume and led to the understanding of how respiration works; i believe this is the correct answer ; /// good luck