In choice (A), we have a run-on sentence, because there is no conjunction between the first independent clause (ending with "desperate for attention") and the second independent clause (starting after the comma). Both clauses are independent clauses because they have subject/verb pairs and they are not introduced by a subordinating conjunction, such as "because." Therefore, we can eliminate choice (A) and also its awkward variant, choice (B).
Choice (C) solves the conjunction problem by providing a conjunction ("and") to join the two independent clauses. Choice (C), consequently, employs proper grammar. This brings us to the question of whether it's conveying the intended meaning of the sentence, and as we'll discuss below, choice (C) is actually not the best option.
In choice (D), the tense of the verb, "having behaved," is wrong; the verb tense indicates that the behavior occurred before some other action, but there is no such action in the sentence.
Choice (E), like choice (C), is expressed with proper grammar. The phrase beginning with "always behaving" is not an independent clause, as in (C); it's a modifying phrase. The two options have slightly different meanings. Choice (C) expresses the two clauses as separate facts. Choice (E) expresses the second portion not as a separate fact, but as something similar to what was just stated--as an elaboration of it. And, in fact, that's exactly the meaning of the latter portion of the sentence; it's an elaboration, not a separate fact, so choice (E) expresses the intended meaning more accurately.
The correct answer is (E).