...enable astronauts to travel ________ space.

• A. In
• B. Into
• C. Through
• D. Across

Answer: (B)

Moving into a new place is shown with into. In space describes a state or location inside space, not the act of entering. Saying travel in space would mean moving while already there, which isn’t what the sentence aims to express. Travel through space or travel across space sounds like moving across space as a path or region, rather than entering it. So, travel into space best conveys the idea of beginning from Earth and entering outer space.