Answer:
The highest mountain
Step-by-step explanation:
This type of superlative shows quality of superiority or inferiority of a noun. The way to identify the absolute superlative is that it doesn't describes the noun in the context of a larger group, it could be said that the description of the noun is definitive and incomparable. For example:
Maria is very smart.
In the sentence is stated that Maria is very smart and is not comparing her to anyone else in a specific group.
Therefore, the correct answer is option B.