Passage Comprehension: Earth's Curvature Observation

This question requires careful reading and understanding of context to fill in the blanks in a given passage. The passage describes an observation that helps demonstrate that the Earth is a globe. It uses the example of a ship sailing out to sea.

Understanding Blank Number 3

Let's focus on the specific blank numbered 3. The sentence leading up to it is: "The bottom of the ship disappears first, and then the ship seems to sink lower and lower..." The part following the blank is: "...we can only see the top of the ship, and then we see nothing at all."

We need a word that connects the continuous sinking of the ship to the point where only its top is visible. This implies a progression that continues up to a certain point.

Analyzing Options for Blank 3:

• 1. since: This word typically indicates a starting point in time or a reason. It does not fit the context of a progression that continues up to a specific outcome. For example, "since we can only see the top" doesn't make logical sense here.
• 2. until: This word indicates the point in time or the extent to which something continues. The phrase "sink lower and lower, until we can only see the top" accurately describes the process. The sinking continues up to the point where only the top part of the ship remains visible.
• 3. by the time: This phrase indicates when something happens relative to another event. While grammatically possible ("...sink lower and lower, by the time we can only see the top..."), it is less direct and natural than 'until' in describing this continuous process leading to a final state. 'Until' emphasizes the duration and the endpoint more effectively.
• 4. after: This word indicates something that happens later in time. It suggests that the sinking happens, and then separately, we can see the top. This contradicts the continuous observation described in the passage.

Based on the analysis, the word 'until' best fits the context, showing the progression of the ship disappearing down to the specific point where only the top is visible before vanishing completely.