The correct option is A You to be
Option B is the correct answer for two reasons. Firstly, it provides an object, i.e ‘you’ to the verb ‘want.’ Secondly, ‘careful’ requires a verb to relate itself to the Pronoun ‘you’ and ‘to be’ is doing that. The verb ‘to be’ is the fundamental verb used to indicate the existence of an entity (person, object, abstraction) or to relate an entity to its qualities or characteristics. Hence, ‘You to be’ is the correct answer. Option B is the correct answer as the sentence is seeking to instruct the other person and hence, usage of ‘be’ is required. Option C cannot be used as it would not bring out the sense of instruction the other person from the meaning of the sentence. Option A and D cannot be used as they would render the sentence incorrect.