Which of the following would MOST effectively reduce risk associated with an increase of online transactions on a retailer website?

Scalable infrastructure helps to handle increased load but doesn't directly reduce the inherent transaction-related risks like fraud or system resource exhaustion that an unbounded increase might cause.

A hot backup site provides business continuity in case of a primary site failure but does not inherently mitigate risks associated with an increase in transactions on the active site itself.

Transaction limits directly address the risk of an overwhelming increase in online transactions by capping the number or value of transactions allowed within a given period, preventing system overload and potential fraud while maintaining stability. This measure proactively controls the 'increase' aspect of the risk identified in the question.

Website activity monitoring identifies issues after they occur or are developing, but it does not proactively prevent risks associated with the raw volume increase like transaction limits would.