Which event in space exploration would appear first on a timeline?
the united states launched its first successful satellite in 1958.
neil armstrong and buzz aldrin made the first manned moon landing in 1969.
cosmonaut yuri gagarin became the first human in space in 1961.
the soviet union launched the first artificial satellite, sputnik, in 1957.

Usually when you do a conclusion, you summarize what was said before, and also by making sure your point went through. So I believe the answer is B. If you restate your introduction (in different words) and with good points, then your whole point would get through. Remember, a conclusion is a closing and is the whole summary of the writing so its best to rephrase but have a good point.