Biology pentose sugars

Hi please could i have help on this question? I know the answer is c or d because pyrimidines are single bases but i thought it would be C because the general formulas of ribose sugars is (CH20)n so there would be a 1:1 ratio between carbon and oxygen atoms?
Here is the question: https://app.gemoo.com/share/image-annotation/629165494436732928?codeId=v67OnOgoJbZgz&origin=imageurlgenerator
Thank you so much!

Hi please could i have help on this question? I know the answer is c or d because pyrimidines are single bases but i thought it would be C because the general formulas of ribose sugars is (CH20)n so there would be a 1:1 ratio between carbon and oxygen atoms?
Here is the question: https://app.gemoo.com/share/image-annotation/629165494436732928?codeId=v67OnOgoJbZgz&origin=imageurlgenerator

Thank you so much!

Adenine pairs with thymine, 1 ring.
It is a DNA base, so is deoxyribose, which has C:O of 5:4. It is D
C was for ribose, which is 1:1.

Hi thank you so much for your reply! I was wondering whether we were supposed to know the structure of ribose and deoxyribose? Also what is the general formula (ch20)n for, why does it not apply here? Thanks!

The general formula applies for ribose.
But the question talks about the nucleotide pairing with adenine in DNA replication, so wanted deoxyribose.
Deoxyribose is ribose with 1 less O.
So instead of 5 carbon and 5 oxygen, giving ribose a ratio of 1: 1, deoxyribose is 5 carbon and 4 oxygen, having ratio 5:4.
You need the know the structures. Similar to how you need to know the structures of alpha and beta glucose.
But once you know ribose, deoxyribose is the exact same except instead of OH on 2’, there is just H.