A statement is a sentence that simply declares or states a fact. It ends with a full stop (.)
A question intends to ask something, and ends with a question mark (?).
A command intends to order someone to do something. It ends with a full stop (.)
An exclamatory sentence expresses a sudden or strong emotion. It ends with the exclamation mark (!).
The given sentence means that the sparkling and dancing waves look very merry in the morning.
This sentence ends with an exclamation mark (!). Hence it's exclamatory. This means that it expresses a strong emotion of joy. So, option D is correct.
It does not state a fact, or ask a question. It does not command anything as well. Hence options A, B and C are incorrect.