When the subject and the object of the verb is the same person or thing, we use a reflexive pronoun.
In the given sentence the subject and the object of the verb is 'the dog'.
The reflexive pronoun for singular third person is 'himself','herself' or 'itself' according to the gender of the noun.
In the given sentence the noun is a dog. So, the reflexive pronoun used must be 'itself'.
Thus option C is the correct answer. Option A and B are incorrect.
The reflexive pronoun for singular first person 'I' is 'myself'. Thus option D is incorrect.