During the data migration testing, you are getting an HTTP error 429 — Too many requests. 
Please select three methods you can use to correct this problem.

Answer options:

A.Use classic flow
B.Use multiple threads
C.Increase service protection limits
D.Minimize API calls
E.Avoid batching

Correct Answers: B, D and
E. 
As a Solution Architect, you need to ensure that Web APIs calls during the data migration process would not hit the API service limits. The API service limits protect the Dataverse service performance and availability. For example, if some users send an extraordinary amount of requests that can affect the other users` operations, the Dataverse limits such a demand for its services. 
The Dataverse service protection API limits are enforced per web server and user. They are based on three measures: Number of requests — the number of requests sent by a user. The limit is 6000 requests within the 5-minute sliding window.
Execution time — the combined time for all requests sent by a user. The limit is 20 minutes within the 5-minute sliding window.
Number of concurrent requests — the number of simultaneous requests made by a user. The limit is 52 requests.
The Dataverse applies all these measures in combination. If you got an HTTP error 429 — Too many requests and a Retry-After header with a number of delay seconds, you have an API service limits problem during the data migration testing. 
You can resolve this problem using the following approaches: Use multiple threads — you can increase the number of threads in your migration tool or use Task Parallel Library with the Web API client.
Minimize API calls — your migration tool should work with Retry-After values to tune the maximum allowed number of Web API calls. You can use .Net code to capture the 429 error and adjust the number of calls in your client library.
Avoid batching — you need to use batches only when you have a transaction type data batch performed on the tables not associated with other tables. In all other cases, keep your calls small as possible to neglect the network latency.
Option A is incorrect because using the classic flows will not help you avoid API service limits.
Option C is incorrect because Microsoft does not allow to increase service protection limits.
For more information about the data migration troubleshooting, please visit the below URLs: 

https://docs.microsoft.com/en-us/learn/modules/power-platform-architecture/6-limits
https://docs.microsoft.com/en-us/learn/modules/project-test-process/3-migrate-data
https://docs.microsoft.com/en-us/powerapps/developer/data-platform/api-limits#how-to-maximize-throughput
https://docs.microsoft.com/en-us/powerapps/developer/data-platform/webapi/execute-batch-operations-using-web-api#when-to-use-batch-requests