Common colds are upper respiratory tract infections. Why are vaccinations against the common cold not practical?
A. Vaccinations do not work in the upper respiratory tract.
B. There are so many different strains of viruses that cause colds it would be impossible to develop a vaccine against all of them.
C. Colds are caused by viruses that cannot be prevented by vaccinations.
D. Vaccines are very costly to develop.
E. Vaccines would not work against the common cold because it is caused by a bacterial infection.
Answer: B
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