The correct order of key events regarding the exploration of space, beginning with the earliest, is:
- First humans in space (Yuri Gagarin in 1961)
- First humans on the moon (Apollo 11 in 1969)
- First lander on Mars (Viking 1 in 1976)
- First space shuttle flight (STS-1 in 1981)
- Hubble Space Telescope launch (1990)
- Last humans on the moon (Apollo 17 in 1972)
However, since the responses you've provided don't align perfectly with this order, the closest correct option given your list is:
First humans in space, first humans on the moon, first lander on Mars, first space shuttle flight.