Why Option A is Correct:Creating a CloudWatch metric filter with "ERROR" as the search term ensures that occurrences of the word "ERROR" in logs are counted. An alarm can then be set to notify the SNS topic when the count exceeds 1. This is the standard approach to monitor specific patterns in CloudWatch Logs.

Why Other Options are Incorrect:

Option B:CloudWatch Logs Insights is used for querying logs manually and does not integrate directly with alarms for automated notifications.

Option C:SNS subscription filters are not a feature for filtering log patterns in CloudWatch Logs.

Option D:CloudWatch alarms do not directly include log filter patterns; a metric filter is needed to create the metric first.

AWS Documentation References:

Creating CloudWatch Metric Filters