Here the issue is with the writes and caching will not solve them. I will go with A and D.

A and D With a workload that is mostly writes and a small number of reads, caching will not be as effective in reducing CPU utilization compared to read-heavy workloads. https://repost.aws/knowledge-center/rds-aurora-postgresql-high-cpu

I will go for A and D, since other options are more likely to improve read performance issues.

A and D. For A it is mentioned here https://repost.aws/knowledge-center/rds-instance-high-cpu

Since the questions states that "the database workload is mostly writes" let's eliminate the options that improves the reads.

Ans. AE A) Use Amazon RDS Performance Insights to identify the query that's responsible for the database load. Check the SQL tab that corresponds to a particular timeframe. E) If there's a query that's repeatedly running, use prepared statements to lower the pressure on your CPU. Repeated running of prepared statements caches the query plan. Because the plan is already in cache for further runs, the time for planning is much less. https://repost.aws/knowledge-center/rds-aurora-postgresql-high-cpu