. What do measles, smallpox and polio have in common? * They are caused by bacteria Vaccines have dramatically reduced the number of people who catch them They are constantly changing They have been wiped out forever

Between Vaccines dramatically reduce infected and they are constantly changing.

Explanation:

All three are viruses not bacteria so a is eliminated, b and c however are both true because their vaccines have drastically reduced the number of infections and they are constantly mutating. The last option d is obviously wrong because there are still laboratories that contain these viruses and could be reintroduced to society.

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