Beta can change over time and can be different between sources. Which of the following is not a reason why betas may be different depending on the source?

A$.$Beta is based on historical values.

B$.$ Beta may be calculated using dfferent periodicities, such as monthly, weekly, or daily.

C$.$The market benchmark may differ.

D$.$Beta may be calculated using $3$ years of data instead of $5$ years of data.