In the following passage some of the words have been deleted. Read the passage carefully and select the correct answer for the given blank out of the four alternatives.

Pumpkins contain high levels of (1) __________. These are molecules that fight harmful free radicals, a (2) __________ of unstable molecule that can sometimes (3) __________ damage to our cells, which may cause ageing and contribute to (4) __________ diseases over time. While some antioxidants occur (5) __________ in our bodies, others we get from fruits and vegetables.