Final answer:
The most effective control to offset the weakness would be option C: The owner reviews credit memos before they are recorded.
Step-by-step explanation:
In this scenario, the most effective control to offset the weakness would be option C: The owner reviews credit memos before they are recorded. By having the owner review credit memos, it provides an additional level of oversight to ensure that credit memos are being properly approved and recorded.
Option A is not as effective because it only focuses on reviewing errors in billings and postings, but it doesn't address the specific issue of credit memos being approved by the accounts receivable clerk with access to cash.
Option B is also not as effective because it addresses the reconciliation of the checking accounts, but it doesn't directly address the issue of credit memos and access to cash.
Option D is focused on reconciling the accounts receivable accounts, but it doesn't directly address the issue of credit memos and access to cash.