Answer:
Smartest
Explanation:
When we want to use an adjective in order to make a comparison between two things, we can either use the comparative or the superlative form. The comparative employs the suffix "-er." Some examples of this would be cleaner, louder or smarter. When the adjective is particularly long, this is substituted by the word "more." Some examples are more powerful, more intelligent, more capable.
On the other hand, the superlative is used to indicate that the object we are talking about has the highest level of such adjective. For this, we would use the suffix "-est" (cleanest, loudest, smartest) or the word "most" (most powerful, most intelligent, most capable).
