Answer:
a. Every film lover should see The Maltese Falcon because it's a classic movie.
Explanation:
All of the other options are grammatically incorrect and/or have incorrect punctuation.
To fix b., you would change it to this:
Do you like movies? If you do, you will love the classic film The Maltese Falcon.
or
If you like movies, then you will love the classic film The Maltese Falcon.
To fix c., you would change it to this:
Be sure to watch The Maltese Falcon. It’s a classic film.
To fix d., you would change it to this:
The Maltese Falcon, a classic movie, is a film every critic should see.
