Correct Answer: Astronaut

Solution : The correct choice is the fourth option.

Explanation:

Astronaut refers to a person who travels in a spacecraft or engages in space travel. It's the most appropriate word in the context of space exploration and travel.

The meanings of the other options are as follows:

• Ghetto: A section of a city, especially a densely populated slum area, often inhabited by a minority group or groups.
• Cadet: A student in training to become an officer in the armed forces or police.
• Voyeur: A person who gains sexual pleasure from watching others when they are naked or engaged in sexual activity, typically in a secretive or intrusive manner.