How much time do you have left to do this ? (I will answer it in the comments)
C because "their" is possessive.
You need to provide more information.
Answer:
The memo should look something like this:
Good morning everyone.
Yesterday I received a complaint from some of our higher management regarding professional conduct and office etiquette. Please keep in mind that, while we all have days when we are not feeling our best, we must make sure that our behavior is befitting the company's reputation.
Manager <u> .</u>
