To reduce function throttling in AWS Lambda, the most operationally efficient solutions are:

1. Increase the function’s reserved concurrency (Option C): Reserved concurrency ensures that a specific number of concurrent executions are always available for your function. This prevents the function from being throttled due to high usage of other functions in your account.

2. Request a service quota change for increased concurrency (Option E): Lambda has default service quotas for the maximum number of concurrent executions across all functions in your account. If the function is throttled due to reaching these limits, requesting an increase in the service quota for Lambda concurrency can help mitigate the issue.