In the sentence, the food of/in/at/by/from McDonalds is unhealthy, I really cannot tell them apart. They all sound correct. The food of McDonalds means McDonald's food, which seems correct. The food is found in McDonalds, so "the food in McDonalds" also seem correct. The same for the other three which all seem correct. Can anyone teach me?
I agree with Copyright, EdisonBhola. "At" is the only preposition that sounds normal to me in that sentence.
"at" is best. "from" is fine for me. But most importantly, you'd invert: McDonald's food is unhealthy. No preposition necessary!
As fun as it is to bash McDonald's, I would say this is too broad. Their menus vary around the world, with salads appearing in many stores and a variety of vegetarian options in India.
Remember that the choice of preposition in English depends very often on physical location, so we'd be inclined to say: Food at/in McDonalds = served at/in their premises Food from McDonalds = bought and taken away from their premises Food by McDonalds = manufactured by them and possibly sold elsewhere. (But does this exist?).
You are right that prepositions are one of the bigger challenges of English -- especially because different prepositions may be used with the same word to create different meanings or nuances. The situation is also confused by what you see in advertising, so while we wouldn't ordinarily say "food by McDonald's," you will see designer or brand-name labels talking about Cristalle by Chanel or The Abington Collection by Timberland and the repetitive Dior Addict by Dior.
How about "food of McDonald's"? I found this sentence from a Google search: Certainly, the “fast food” of McDonald’s and similar companies are not alone in their unhealthiness, but the contention that they are perfectly healthy is horrendously misleading and incorrect. Does it sound good to you?
No. It's awkward, has subject-verb disagreement, bad preposition choice, etc. etc. Blogs and general forum chat should never, ever, be used as a guide to the English language.
