Answer:
C. The dam would be taller than any dam in the world.
Explanation:
The structure of comparative sentence is: Noun 1 + be + Comparative Adjective + than Noun 2.
=> The sentence is used to compare Noun 2 and Noun 2.
In the sentence "The dam would be taller than any dam in the world.", "The dam" is Noun 1, "any dam in the world" is Noun 2. In addition, there is "taller" - the comparative form of adjective "tall" and preposition "than"
=> The sentence compare the tall/ height of the dam with the other dam in the world.