I would go with D. The other three don't really make sense..... So, The answer is D.
He learned how strong and powerful
Myself would be considered an intensive pronoun for it adds emphasis to the subject of the sentence
It is a declarative sentence as it is making a statement.
Interrogative- question (?)
Imperative- request/order/advice
Exclamatory- surprise (!)
Declarative- simple statement
