What do activity file parameters establish for issuers?

Activity file parameters are critical for issuers as they define specific limits concerning the management of account activities. These parameters are set to establish constraints on both the frequency (number) and financial value of transactions that can be authorized on a cardholder's account. By setting these limits, issuers can mitigate risks associated with fraudulent transactions, increase the safety of cardholder accounts, and ensure compliance with regulatory requirements.

In contrast to the other options, which address different aspects of financial operations, such as marketing strategies or merchant account setups, activity file parameters are primarily focused on the security and authorization of transactions themselves. This direct correlation to transaction controls is what makes option B the correct answer.