This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Dental
The edge of a cutting hand instrument is rested on a dental tray, which causes it to slide. What does this determine? 
Select and explain. 
A. The instrument is unbalanced, B. The instrument is dull, C. The instrument is very heavy, D. The instrument needs to be replaced
B: The instrument is dull
Answer: B: The instrument is dull 
Explanation: Sharpness Test:

It is a method of testing the sharpness. Sharpness of an instrument can be tested by lightly resting the cutting edge on a hard plastic surface.  
If the cutting edge digs in during an attempt to slide the instrument forward over the surface, the instrument is sharp. 
If it slides, the instrument is dull. Only very light pressure is exerted in testing for sharpness.

Ref: Sturdevant's art and science of operative dentistry. 4th edition page 321