What is the most effective way to increase the oxygen content of air ?

Select the correct answer from each drop-down menu proteins are

Vaccines are weakened forms of disease causing microorganisms, which are given to patients to prevent disease. after the vaccine is administered, the immune system responds by creating a(n) to recognize the a.) antibody, antibiotic b.) antigen, antibody c.)antibiotic, antibody d.)antibody, antigen

Which of the following is an eon in the time scale? phanerozoic proterozoic archean all of the above