Antibodies are found in mucosal secretions and to protect the respiratory system from infection.

IgA antibodies are found in mucosal secretions and help to protect the respiratory system from infection .

Explanation:

Immunoglobin A or IgA is found in the mucous and other secretions like tears, saliva, and breast milk. It takes part in the body’s immune system and protects against pathogens like bacteria and viruses. These secretary immunoglobins represented as sIgA is exclusively present in respiratory epithelium. IgA deficiency may cause respiratory illness like sinusitis, asthma, bronchitis, pneumonia etc. upper and lower respiratory tracts are mostly affected with less pathogenic viruses or bacteria and patients are most affected when they are combined with single antibody deficiency of IgA .

A

Explanation:

Fertilizations occurs in the fallopian tube.

Point "a" is located where the fallopian tube is at

Hence, fertilization is most likely to occur at point A