Alibaba Cloud Certified Associate (ACA) Practice Test 2025 – Complete All-in-One Guide for Exam Success!

The reason the first option is correct has to do with the API's requirement for input parameters to function properly. The ModifyDBInstanceSpec API call is designed to change the specifications of a given database instance. If the request does not include an instance type, the API lacks the necessary information to process the modification. Essentially, the absence of a required parameter means that the API cannot correctly understand what modification is being requested, which results in a failure of the call.

In contrast, although an instance running a scheduled backup may cause delays or restrict certain operations, it does not necessarily result in a failure of the API call; the call may still be processed once the backup is complete. Similarly, if the targeted RDS instance is already at peak specifications, it may not allow further modification, but it wouldn't cause the call to fail outright; rather, it would indicate that no changes can be applied. Lastly, making a request on a public holiday does not influence the ability of the API to process requests, as cloud services generally operate continuously regardless of calendar dates.