Answer: Creating the advertising message
Explanation: What Julian is doing is creating an advertising message as part of an advertising campaign. A campaign can be composed of, for example, a series of advertising messages that are similar or different but have one in common to promote a particular product or service. As such, all of these messages form one integral marketing unit within the campaign.
In particular, Julian is in the process of creating an advertising message. An advertising message can be composed of words, which Julian has already done, it is an advertising slogan, and it can also be composed of illustrations, visuals and sound recordings. As the advertising message can contain any of the media presenting the message, so can the combination of multiple media, in this case, an illustration and words, because it is a form of advertising message that can be found in the magazine. So Julian is in the making of an advertising message because he is working on what illustration to use to complement the words he has already assigned to the message.