the OE states this:
A campaign cannot be targeted to someone; it must be targeted at someone. This sentence is not idiomatically correct; the preposition to must be changed to the preposition at.
When answer choices differ because they use different prepositions, focus on the expression in which the preposition is used, and try to recall the list of common idioms. This campaign has two targets, young supporters and older fans. These targets must be introduced by the preposition at.
Choice C changes to to at; the campaign is targeted at young supporters and older fans. This change fixes the idiomatic error without introducing additional errors. The answer is C.
Choice B changes to to at in order to introduce the first group, the young supporters. However, by inserting for before the second group, choice B creates a new idiomatic error. Targeted...for older fans is not correct. When an idiom applies to more than one item in a sentence, as it does here, make sure that all items that use the idiom are correct.
Choice D uses targets of, which is equally as unidiomatic as targeted to or targeted for
Choice E retains the idiomatically incorrect targeting to.