Final answer:
The correct answer is a; no planet other than Earth in our solar system can support human life without protective gear due to hostile environments like incorrect temperature, a lack of breathable atmosphere, and unsafe pressure levels.
Step-by-step explanation:
The answer to the question 'On which of the planets (other than Earth) could a human being step out of a spacecraft and survive without any protective gear?' is a. You can't fool me; there is no other planet on which we could survive unprotected.
No other planet in our solar system has an atmosphere that is breathable by humans, nor do they have the necessary pressure or temperatures conducive to human life. Protective gear is essential for any manned space mission due to hostile environments, and should a spacesuit rupture on planets like Mars or Venus, survival chances without immediate corrective action are virtually nil.