Humans are protected by some infections by specialized cells which produce chemicals that ... a - destroy microbes

b - recycle nutrients

c - allow locomotion

d - coordinate movement

The answer is the option a. Humans are protected from some infections by specialized cells wich produce chemicals that destroy microbes. Those cells are white blood cells, also named leukocytes. Leukocytes attack bacteria, viruses and germs to protect our body from infectious diseases.