A. Mistake in balancing an account
B. Omitting to record a transaction entirely in the subsidiary books
C. Recording of a wrong entry in the subsidiary books
D. Posting an entry on the correct side but in the wrong account

A. The mistake in balancing an account affects the agreement of a Trial Balance A. is the
correct answer. The other mistakes do not affect the agreement of Trial Balance. The omission to
record a transaction entirely in the subsidiary books B. will not affect the agreement of a Trial
Balance because both the aspects of a transaction are omitted to be recorded. Recording of a
wrong entry in the subsidiary books (c ) will not cause disagreement of a Trial Balance because,
the wrong entry so recorded has the effect of posting the transaction in the manner it is recorded.
Posting an entry on the correct side in the wrong account D. does not affect the tallying of a Trial
Balance because the aspect of the transaction is posted to the correct side of an account. Thus
A. is the correct answer.