I don't get the answer. If you read the question on the website (not in the email, but on the website, it asks: "Largest Unit

How much information does a Yottabyte store? (check all that apply)"

The answer in Wikipedia is both 1000^8 and 1024^8:

"When used with byte multiples, the SI prefix may indicate a power of either 1,000 or 1,024, so the exact number may be either:

1 septillion, or 1,000,000,000,000,000,000,000,000 bytes — 10008, or 1024, or

1,208,925,819,614,629,174,706,176 bytes — 10248, or 280.

The term "yobibyte", using a binary prefix, has been proposed as an unambiguous reference to the latter value."

so why not all answers are correct?