The use of pronoun is “its” is essential in the above case because dog is a noun and wagged its tail as soon as the food dish was filled (past tense).
Therefore, pronoun is clearly connects the sentence with meaningful form and with a grammar form.
Thus, the options (d), (b) and (a) are incorrect.
The use of pronoun is “its” is essential in the above case because dog is a noun and wagged its tail as soon as the food dish was filled (past tense).
Therefore, the correct option is – c. its.