a. a field of spinachb. a large, scrap metal junkyardc. a one half mile deep deposit of iron ored. iron deposits on the iron floore. none of these answers
go with what richard s is telling you . plus as long as the service write up on your car is still open you can drive past the warranty end date and it will still be covered
Do you want to eat it, or make something from it? A field of spinach would contain a minuscule amount of iron, compared to the other options (spinach is 80% water, to start with); but would be edible. Probably a hectare of spinach would contain about 10 kilograms of iron A scrap yard of a hectare or so would contain about thousand tonnes of iron. A one half mile deep by one square mile deposit of high grade iron ore say 50% iron, would contain in excess of a billion tonnes of iron. If you mean Iron deposits on the ocean floor; these would be several orders of magnitude greater than an iron ore deposit; and contain a trillion tonnes of iron or more; but would only be about 5% iron, and uneconomic to recover. So, seeing as you asked for the 'highest quality', then an iron ore deposit would win hands down. That is; unless you wanted to eat it. In that case; a couple of beef carcases would contain about ten times as much iron as a field of spinach.
I think they're b.s.ing you.