Data Factory keeps pipeline-run data stored only for a specific time. Using Azure Monitor is the best option If you desire to keep the data for a longer time. By default, how long are the Azure Data Factory diagnostic logs retained for?

Answer options:

A.10 days
B.15 days
C.40 days
D.60 days
E.None of these

Correct Answer: E 
Pipeline-run data is stored by Data Factory only for 45 days. Using Azure Monitor is the best option If you desire to keep the data for a longer time. Azure Monitor, diagnostic logs can be routed for analysis to many different targets.
Option A is incorrect. Pipeline-run data is stored by Data Factory for 45 days, not 10 days.
Option B is incorrect. Pipeline-run data is stored by Data Factory for 45 days, not 15 days.
Option C is incorrect. Pipeline-run data is stored by Data Factory for 45 days.
Option D is incorrect. Pipeline-run data is stored by Data Factory only for 45 days, not 60 days.
Option E is correct. Pipeline-run data is stored by Data Factory for 45 days.
Reference: 
To know more about monitoring Data Factory, please visit the below-given link: 

https://docs.microsoft.com/en-us/azure/data-factory/monitor-using-azure-monitor