Meaning: 'At' indicates a specific point or location, in this case, the bottom of the frames.

Wrong options:

• arrives: The verb 'arrives' does not fit grammatically as it implies movement towards a place, which does not apply to the context of thickening.
• off: The preposition 'off' suggests separation or distance, which does not relate to the context of thickening at a specific location.

Correct answer: diminishing

Explanation: The gerund 'diminishing' describes the action of decreasing in thickness, which fits grammatically and contextually as it parallels the thickening mentioned earlier.

Meaning: 'Diminishing' means to decrease or lessen in size or amount.

Wrong options:

• arrives: The verb 'arrives' does not fit as it does not convey a sense of reduction or decrease in thickness.
• off: The preposition 'off' does not relate to the concept of thickness and does not fit in this context.

Correct answer: intriguing

Explanation: The adjective 'intriguing' describes the phenomenon as interesting or fascinating, which aligns with the context of discussing a curious occurrence.

Meaning: 'Intriguing' means arousing curiosity or interest.

Wrong options:

• arrives: The verb 'arrives' does not fit as it does not describe a quality of the phenomenon.
• figuring: The gerund 'figuring' does not appropriately describe the phenomenon and does not fit grammatically.

Correct answer: flows

Explanation: The verb 'flows' indicates the action of moving steadily and continuously, which fits contextually as it describes how the glass behaves over time.

Meaning: 'Flows' means to move or run smoothly in a continuous stream.

Wrong options:

• arrives: The verb 'arrives' does not fit as it implies reaching a destination rather than a continuous action.
• off: The preposition 'off' does not relate to the action of movement and does not fit in this context.