The correct answer is option (D):
No change
The correct answer is "No change" because the original sentence, "Mount Blanc is the highest mountain in the Alps," is grammatically correct and accurately describes the geographical fact. Let's break down why the other options are incorrect:
* "a higher mountain in the Alps": This option uses the comparative adjective "higher." While Mount Blanc is higher than most mountains, the sentence isn't making a comparison; it's stating its superlative position (the highest).
* "a highest mountain on a Alps": The phrase "a highest" is incorrect. The superlative adjective "highest" requires the definite article "the." Also, "Alps" is a plural noun referring to a mountain range and therefore does not take the article "a". The correct preposition to use is "in" rather than "on" to specify its location.
* "the highest mount of the Alps": Although "highest" is correct, "mount" is a less common and slightly informal term than "mountain." While both refer to the same thing, the original sentence is more standard. "of the Alps" is grammatically correct but the original "in the Alps" is also correct.
Therefore, the original sentence is the most accurate and grammatically sound option.