The correct option is
A An advertisement for a travel agency aimed at students
Non-classified display ads are advertisements (in a newspaper) that do not have any limit when it comes to space, or placement. Such ads are usually by large companies or brands and have their own customized design and display, to advertise their product or service.
Display ads can be classified or non-classified. Classified ads have a limit in terms of space and placement. In both cases, display ads are meant to be visually appealing, and attract the attention of the reader more than the worded advertisements. Hence, they cost more than classified text ads.
Option A: Advertisements for travel agencies can be visually appealing, by including a picture of the destinations and happy students' faces. Hence it's an example of a display advertisement and option A is correct.
Option B: A job opening ad cannot be visual. Job openings are usually advertised on a lower budget because they don't want to sell, but employ.
Option C: The sale of old furniture is made through small-scale vendors or it can be someone's personal property on sale. Such an ad does not invest a lot in displaying the product.
Option D: A to-let is an ad for an apartment on rent or lease. It does not require a display.
So, these options are not display/non-classified ads
Hence options B, C and D are wrong.