A.I. Explanation:

Option 1: "increasing"

Explanation: The term 'increasing' does not accurately describe the movement of a glacier as presented in the text. The text emphasizes the glacier's movement as a slow process, which is better captured by the word 'flowing.' Therefore, 'increasing' is misleading and does not align with the context of the glacier's gradual movement.

Option 2: "flowing"

Explanation: The correct answer 'flowing' directly relates to the description of the glacier's movement in the text. The phrase 'this river of ice is (flowing)' indicates that the glacier is moving, albeit slowly, which is consistent with the overall theme of the text. The use of 'flowing' captures the essence of how glaciers behave, making it the most suitable choice.

Option 3: "expanding its reach"

Explanation: While 'expanding its reach' suggests a form of movement, it implies a broader and more aggressive action than what is described in the text. The text focuses on the glacier's slow movement rather than an expansion, making this option inaccurate in the context provided.

Option 4: "freezing over"

Explanation: The phrase 'freezing over' contradicts the idea of movement presented in the text. Instead of describing the glacier's motion, it suggests a state of stillness or inactivity, which does not align with the context of observing the glacier's movement through time-lapse photography.