a. You.
"You need to plan ahead,"she said, "because there are many fascinating attractions to choose from."
Capitalization is writing the first letter of the sentence in Uppercase and the rest in lowercase, unless, the word within the sentence is a proper noun.
Rule 1. Capitalize the first word found in a document or found after a period.
In the sentence, the first word is You. That is why its first letter is in uppercase and the rest of the words in the sentence are in lowercase.
