Select from options: Continue writing the next sentence.

How to spell numbers
Spell out the numbers one through nine.
Unless you are short on space, this is the most widely accepted way to write a single-digit number.
Spell out " zero " as well.

Select from:
(a). If you are short on space, this would be incorrect for the total sums of both digits. This is true even for figures of two or more digits.;
(b). The numbers zero, zero, one, and nine all play an important role in the multiplication process, and may even appear in the cockatoo's mind when the digits are added together. Therefore, just use that phrase " zero " to spell the numbers accurately.;
(c). You may also spell it as " zed " if using the uk english accepted spelling. Since it can be easily mistaken for the letter " o " it is best to treat it as if it were a single-digit number.;
(d). If you have any space left, use this to write the letters "-. " Spell out numbers one through nine.;
Answer:
(c).