Meaning: 'Orbiting' means moving in a curved path around a planet or star, in this case, the ISS moving around Earth.

Wrong options:

• postponing: Postponing means delaying something, which does not fit the context of the ISS's function in space.
• tabulating: Tabulating refers to arranging data in a table, which is unrelated to the ISS's movement around Earth.
• investigating: Investigating means examining or inquiring into something, which does not accurately describe the ISS's primary action in relation to Earth.

Correct answer: joint

Explanation: The term 'joint' accurately describes the collaborative nature of the ISS project, involving multiple space agencies. It fits grammatically as an adjective that modifies 'project' and contextually emphasizes the cooperation among different nations.

Meaning: 'Joint' means shared or done by two or more parties together, highlighting the collaborative effort in building the ISS.

Wrong options:

• predominant: Predominant means most important or powerful, which does not convey the collaborative aspect of the ISS project.
• solemn: Solemn refers to something serious or grave, which is not relevant to the nature of the ISS as a collaborative project.
• solitary: Solitary means alone or single, which contradicts the idea of multiple agencies working together on the ISS.

Correct answer: has since

Explanation: The phrase 'has since' is the correct present perfect form that indicates an action that started in the past and continues to the present. It fits grammatically and contextually, as it describes the ongoing occupancy of the ISS since its first inhabitation.

Meaning: 'Has since' means that from a specific point in the past (November 2, 2000), the action of being occupied has continued up to now.

Wrong options:

• having since: 'Having since' is grammatically incorrect in this context as it does not form a complete verb phrase for the intended meaning.
• since have: 'Since have' is incorrect because it disrupts the proper tense structure needed for this sentence.
• since having: 'Since having' is also incorrect as it does not convey the ongoing action appropriately.

Correct answer: altitude

Explanation: The word 'altitude' correctly refers to the height of the ISS above Earth's surface, fitting grammatically as a noun that describes a measurable distance. It aligns contextually with the sentence, which discusses the ISS's position in space.

Meaning: 'Altitude' means the height of an object in relation to sea level or ground level, in this case, the height of the ISS above Earth.

Wrong options:

• latitude: Latitude refers to the geographical coordinate that specifies the north-south position on Earth, which does not relate to the height of the ISS.
• float: Float means to rest or move on the surface of a liquid, which is not applicable to the context of the ISS's height above Earth.
• pace: Pace refers to the speed of movement, which does not describe the vertical distance of the ISS from the Earth's surface.