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Help the amateur office detective complete her notes about the missing chocolate cake by selecting the most logical modal verbs.
"Look at Dave! He has chocolate frosting all over his mouth. He _________________________ be the thief!
But Sarah is severely allergic to chocolate, so she _________________________ be the culprit.
What about Jim? He's looking a little bit nervous in the corner, so he _________________________ know something about it. I'll interrogate him next!"
must
We use must when we are almost entirely sure something is true based on present evidence (Dave has frosting on his face).
can't
We use can't when we are almost entirely sure something is NOT true (Sarah is allergic, so it is impossible that she ate it).
might
We use might (or may/could) when we think something is possible but we aren't completely sure (Jim looks nervous, which is a clue, but not absolute proof).