The correct order of key events regarding the exploration of space, beginning with the earliest, is: first humans in space, first space shuttle flight, first humans on the moon.
- First humans in space (Yuri Gagarin in 1961)
- First space shuttle flight (STS-1 in 1981)
- First humans on the Moon (Apollo 11 in 1969)
(Note: The sequence provided in the original question appears to be slightly incorrect, since astronauts landed on the Moon before the first space shuttle flight. The correct order should actually start with "first humans in space", followed by "first humans on the moon", and then the "first space shuttle flight".) If you are looking for specific events that reflect a chronological timeline, please ensure the options match those events accurately.