You have passed all your tests. You must be very pleased with yourself. Here option C is correct.
In this context, the sentence structure suggests a positive outcome or achievement, indicating that the person being addressed has successfully passed all their tests.
The use of "must" conveys a strong recommendation or conclusion based on evidence. When expressing satisfaction or congratulating someone for a positive accomplishment, "must" is appropriate because it emphasizes the certainty of the feeling.
It implies that the person is logically expected to be pleased with themselves given the successful test results. Here option C is correct.
Complete question:
You have passed all your tests. You ____ be very pleased with yourself.
A - mustn't
B - should
C - must
D - shouldn't