Final answer:
Urea should be heated above 50°C to inactivate bacterial enzymes.
Step-by-step explanation:
Urea should be heated above 50°C to inactivate bacterial enzymes (C). Urease is an enzyme that hydrolyzes urea to ammonia and CO₂. By heating the urea above 50°C, the enzymes responsible for this reaction are denatured, rendering them inactive. This is important in certain laboratory tests, as it allows for the detection of ammonia (produced by the hydrolysis of urea) in the presence of bacteria.