Hi. I saw this question, but now I can't find it. I don't want to post a new question when it duplicates. Which question asked why after a verb, some nouns can be singular BUT some singular nouns must have an article. This is like
ell.stackexchange.com/q/300702. Examples ✓ I have concern, I have concerns, I have difficulty, I have difficulties. I have apples. ✓ But X I have apple. X