Question

the orbit in london, england, is the worlds tallest tube slide. it is as tall as a 25 - story building. from the base, which is the ground level, an elevator carries people up to the top. which of these clues helps you understand what base means?

Explanation:

The phrase "which is the ground level" is a direct definition or clarification of the word "base". It provides context to help understand what "base" means in this context.

Answer:

which is the ground level