The Wizard of Oz. It's the title of the book.
B. the same line you left off. however, make sure to reference in accordance with the type of paper you are doing, apa or mla
It causes a little confusion to have that "Blank Space" right after the the main verb "expect" because we cannot be sure that it represents that a blank or a space is that follows, or that Blank Space is used as a noun.
To answer this question I will assume that blank space represents that a line goes there to be filled.
By doing so, the correct sentence would be:
Joel and Lucy expect _their_ Halloween party to be really scary!
So the final answer is:
Their
The possessive third person plural pronoun is the best option.