I have been posed with a question in an economics class at college which I cannot decipher: "Explain how an increase in the price level affect the real value of money. Give a real world example."
I emailed the instructor to ask for clarification, asking if he missed a plural somewhere or made a typo, and he advises me as follows: "It is not missing a plural – simply read it as price level affects."
Would it written as “Price level affects” not be plural? Is it possessive rather than plural? Slippery slope? I want to write him back, but worry I may not truly have a full grasp of the grammar and English complexities involved. Is there is some grammatical rule I do not know which dictates that words (or specifically, the word affect) no longer need to be made plural to be read as plural? Is adding an "s" to affect to make it affects in this case not making it plural? What am I missing?