Suspense account

Question:
The suspense account shows a debit balance of $100. What could this balance be due to?

A Entering $50 received from A Turner on the debit side of A Turner’ s a/c.
B Entering $50 received from A Turner on the credit side of A Turner’ s a/c.
C Undercasting the sales day book by $100.
D Undercasting the purchases a/c by $100.

The question ask me what is the reason for this difference between debit side and credit side of Trial balance.

(1) I have read your answer before that correct choice is D.
(2) I also know A, B, C is incorrect answer in this question.
But I am still confused about the answer because of the following reasons:

– First, I think “debit balance” in any accounts means that Total CR > Total DR in this account (ie “debit balance” of $100 in suspense account meaning CR suspense account $100; T-account for it is: T-account (suspense account) — DR side: — CR side: b/f $100)
– Second, when undercasting the purchases a/c by $100, the double entry will be:
DR Suspense account $100 / CR Payables $100
– Third, in the second reason, I have debited Suspense account. So in this case, I think Suspense account has Total DR > Total CR, which contradicts first reason.

Please check the accuracy of my thinking, thank you so much.