Hi Your sentence is fine as it stands. If you were referring back to a previous phrase or sentence, you could use 'the' if you wanted to: - We were concerned about a lack of understanding of HPV. Indeed, our study revealed the low levels of knowledge about curing HPV If you wanted to, you could use 'a' with the singular: - Our study revealed a low level of knowledge about curing HPV But,as said, your original sentence is OK Dave
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