The sentence, "Flora flew a yellow kite" is a completed thought because it has a subject, a verb, contains a clause and ends with a punctuation mark which was a period in this case.
It is not a subject because a subject is the performer of the action in a sentence, and it is also not a verb because a verb is an action word, however, it contains a subject and a verb and contains a completed thought.
The correct answer is B. It's B. because, the other sentences don't make sense, and they are improper, the other choices are also not the proper way to speak.
