There _______ be some mistake. I didn't order any appetizers, and yet you're charging me for them.
must
She hasn't seen my texts. She _________ be in the shower.
must
It _____ be a fight. Everyone is laughing. They _____ be celebrating really loud.
can't/must
Mary never meets her deadlines, and she still insists on starting a new project every week. She _____ know better.
should
We don't know how bad the skiing accident was. If her leg was injured, her career ______ be ruined.
could
He _______ have a good job. Check out the car he arrived in.
must
