Question

Most of the film wasn't as exciting as _____ beginning. (Points : 1) A. their B. theirs C. its D. it's

Answer 1

Answer C. its.

Most of the film wasn't as exciting as its beginning. 

I chose C. its because the word 'their' or 'theirs' refers to one or more than one person(s) item or pet. Example: "The cat was theirs."
Example 2: "Their horse watched from the pen." 

And answer D. it's, also refers to something that someone is in possession of, or describing. 'It's' is short for 'it is'. 
Example: "It's a beautiful necklace." 
Example 2: "It's rightfully her car."