The correct order of key events regarding the exploration of space, beginning with the earliest, is:
- First humans in space (Yuri Gagarin, 1961)
- First humans on the moon (Apollo 11, 1969)
- First space shuttle flight (STS-1, 1981)
So the appropriate response would be:
first humans in space, first space shuttle flight, first humans on the moon.
(Note: "first humans on the moon" and "first space shuttle flights" are not in the options listed, so please choose the response that aligns with the correct chronological sequence provided in the alternatives.)