A.I. Explanation:

Option 1: "It had completed all its research objectives."

Explanation: While the Cassini spacecraft has achieved many objectives, the text does not state that it has completed all of them. Therefore, this option is misleading as it implies finality that is not supported by the text.

Option 2: "To prevent contamination of Saturn’s moons."

Explanation: The text mentions protecting the moons of Saturn, but it does not specify that the primary reason for the planned end was to prevent contamination. This option misinterprets the text's intent.

Option 3: "It was no longer able to transmit data back to Earth."

Explanation: The text does not indicate that the Cassini spacecraft is unable to transmit data. It states that it is running out of fuel, which is a different issue. Thus, this option is incorrect.

Option 4: "The spacecraft is running out of fuel."

Explanation: The text clearly states that after 20 years in space, NASA's Cassini spacecraft is running out of fuel. This directly supports the reason for planning a spectacular end, as it indicates that the spacecraft can no longer continue its mission effectively.