Final answer:
The correct adverb to describe how someone dresses is 'smartly,' making option C the right choice in the sentence 'My mother usually dresses smartly.'
Step-by-step explanation:
The correct answer to the question "My mother usually dresses [...]" is C, smartly. When describing how someone dresses using an adverb, 'smartly' is the appropriate choice. 'Smart' is an adjective, and while it can describe a person, it is not used to describe the action of dressing itself in this context. 'Smartful' is not a word in standard English usage. The option 'most smart' would not be grammatically correct in this sentence.
Using 'smartly' suggests that your mother dresses in a neat, clean and fashionable manner, which is often associated with intelligence and sophistication. It's wonderful to hear how you hold your mother in high regard, describing her as loving, supportive, and having taught you everything you know, much like the lady in the snippet from Daisy Miller who is affectionately connected with her daughter's belongings.