Border marks where a country is : a country is encompassed by borders. This is similar to ocean and shores: shores mark where the ocean is: an ocean is encompassed by the shores.
The answer is d.
The anwer is D) My primary quibble with ear buds is that they are very distracting devices and are therefore dangerous.
This is the sentence that would best serve as a topic sentence for this passage. In the passage, the author focuses on the fact that ear buds can be very distracting. He presents several examples of why this is the case. Moreover, he argues that ear buds can be dangerous, for example, when someone is driving. Option D discusses both of these facts, and therefore, fits the best with the paragraph.
Answer:
America is the only.country that uses the metric system
I think it is because the answer choice "A" does not provide an explanation for why everything tasted sweet, leaving the reader wondering. D, however, gives an explanation.