中四ACCOUNT--Suspense accounts and errors

Which of the following errors would affect the agreement of a trial balance?

A. The total of a purchases invoice was undercast.
B. Purchases from T Lee were entered in C Lee's account.
C. Carriage outwards were debited to carriage inwards account.
D. The total of the sales account was overcast.

The answer is D.
我想問
1. A點解唔會影響agreement of a trial balance？
2. 在ans A中，"invoice"呢個字包含左d什麼意思？
3. ans C 點解唔會影響agreement of a trial balance？

唔該~