Final answer:
The subject of the question is English. The correct answer is Theird.
Step-by-step explanation:
The subject of the question is English. The correct answer is Theird. In the given sentence, the subject is 'dog', which is a singular noun. Therefore, the correct pronoun to use is 'their' in the possessive form, making the sentence 'Their dog barked loudly all night, keeping the neighbors awake'.