As an ESL teacher, I am currently teaching the topic on nouns as adjectives. Some examples are shoe shop, boat-race, apple tree, etc. One of the rules of nouns as adjectives that I have learnt is that when nouns are used an adjectives, they are usually in singular form. Some cases that seem like exceptions but aren't really, are news reporter and sales manager, as we all know that news and sales are really singular nouns ending with an s.
But for these other job titles, Systems Analyst and Systems Manager, could anyone give me a clear explanation on why we use the plural form systems instead of its singular form before I resort to telling them it's an exception?
