The correct answer is A. Better
Step-by-step explanation:
In grammar, there are mainly two ways of describing the object of a group about other objects that belong to the same group. The first one is by using the superlative that states one object is the best or has a unique quality over others of the same group and that is formed by adding "-est" to adjectives or "most" before the adjective in cases the adjective is long; for example, this house is the biggest of the neighboorhood.
The second way is by comparing objects in which one object has a certain degree over another and that is formed by adding "-er" or "more" before the adjective in case of long adjectives and that in most cases is followed by the word "than" that stablishes the comparison, for example, Carla is taller than me. This implies in the case of the sentence "Some stocks are more expensive than others, but this stock performs _____ than most" due to the word "than" the comparative form rather than the superlative should be used and considering the adjective is short the correct form is "better" as this expresses a comparison between this stock and other stocks.