Final answer:
The correct option is A. All astronauts visiting the International Space Station must learn Russian because it is essential for communicating with Russian-speaking crew members and operating the Russian Soyuz spacecraft that transport astronauts to the ISS.
Step-by-step explanation:
The language that all astronauts visiting the International Space Station (ISS) must learn is Russian. Since the early days of the ISS program, Russian has been the primary language used for communication between astronauts and cosmonauts.
This is because Russia plays a significant role in the operation of the ISS. Russian spacecraft, such as the Soyuz, are used to transport crew members to and from the ISS. Additionally, many of the station's important systems and equipment were developed by Russian space agencies. Learning Russian helps facilitate communication and collaboration during space missions, ensuring the safety and success of the crew on board the ISS.