Choice a : Explains what the nations need to do and elaborates some.
--wrong answers--
Choice b only gives a statement of what the nations need to do.
Choice c is a question.
Answer:
(I'm not entirely sure) I believe that the one you marked in the photo is the correct option (#3). Otherwise, it would become a run-on sentence.
The correct answer is letter A
Human kinds ideal setting was in the 1800 and 1850