Okay, this is a throwback to AP biology my senior year of high school. The correct answer is A: domain, kingdom, phylum, class, order, family, genus, species. Most people will get that the domain is the largest, and genus and species are the smallest, in that order, because that’s how we tend to remember things - the beginning and the end.
I was taught a mnemonic to remember this: Dear King Phillip Came Over For Good Soup. The first letter in each word is the same as the first letter of the classification level.
This is especially helpful for those who tend to forget the order because each level starts with a different letter. Remember this and you’ll never have to struggle with this order again.