Question

who began the fight against smallpox in 1967 and by 1979 the organization was able to declare the world free of the disease. who began the fight against smallpox in 1967, and by 1979, the organization was able to declare the world free of the disease. who began the fight against smallpox in 1967, and by 1979 the organization was able to declare the world free of the disease. who began the fight against smallpox in 1967 and, by 1979 the organization was able to declare the world free of the disease.

Explanation:

In English grammar, a comma is often used to separate clauses in a compound - sentence for better readability. The first option has a comma after "1979" which is a correct usage to separate the two related but distinct parts of the sentence. The second option lacks the comma after "1979" which makes it less grammatically correct in terms of punctuation for this type of sentence structure. The third option has an incorrect comma placement after "and".

Answer:

WHO began the fight against smallpox in 1967, and by 1979, the organization was able to declare the world free of the disease.