The answer is C: Their apartment has a lovely view of the park.
Here are the reasons why the other answers are incorrect:
A.Theyre apartment has a lovely view of the park. The word "Theyre" is not a correct word.
B. There apartment has a lovely view of the park.The word "There" is used to refer to a place, i.e They went THERE to get icecream.
D. They're apartment has a lovely view of the park. The word "They're" is short for They are, so thats why it doesn't make sense!
