Final answer:
Horseradish is the only option that can be ingested prior to a fecal occult blood test.
Step-by-step explanation:
The only option that can be ingested prior to a fecal occult blood test is horseradish. The test is done to detect hidden blood in the stool, and certain substances can interfere with the test results. Vitamin C, aspirin, and spinach are known to affect the accuracy of the test, so they should be avoided.