Respuesta :
The answer should be, "Big", or "Giant". Unless there are options to choose from, something like the two examples given should be correct, because the tone has changed from a simple walk to a disastrous one.
The word type that would best complete the sentence is an adjective.
An adjective is a describing word and modifies a noun. In this case, the adjective is modifying the word "boulders." An example sentence would be, "But soon, we were scrambling over gigantic boulders and scaling walls of stone." However, any adjective that accurately describes the boulders could be used.