Question: Keeping the observer and the cup geometry unchanged, only replace the transparent liquid to be poured into the cup. To make a previously invisible small target inside the cup become visible for the first time with the minimum liquid level, which of the following replacements is most suitable?
A. Glycerol
B. Ethanol
C. Acetone
D. Physiological saline (saline solution)
Clues:
1. A sequence of four images shows a white mug against a black background.
2. In the first two images, a coin is shown falling into the mug.
3. In the third image, the mug is empty, and the bottom of the mug is not visible from the camera's angle.
4. In the fourth image, the mug contains a transparent liquid, and the coin is now visible at the bottom.
5. The visibility of the coin at the bottom of the mug is dependent on the presence of a liquid inside it.
Answer: A
Category: Physics