Which formats can be used to add a custom campaign parameter to a URL?

The correct answer is the format that adheres to the conventions established for UTM (Urchin Tracking Module) parameters, which are used to track the performance of marketing campaigns in Google Analytics. The format must be a properly structured query string where the parameter name is followed by an equals sign and then the value without any spaces.

In the first option, the URL correctly includes the UTM campaign parameter as utm_campaign with an equal sign followed by the value fallsale, satisfying the correct format for campaign tracking. This allows Google Analytics to correctly interpret and categorize the traffic coming from this URL, enabling accurate reporting on campaign performance.

The other formats include incorrect spacing or the absence of an equal sign, which would render them unusable for tracking purposes. This makes www.googlemerchandisestore.com/?utm_campaign=fallsale the only option that correctly follows the UTM parameter structure needed for campaign tracking in Google Analytics.