A. Avian Oculars weigh less than traditional binoculars.

The argument does not assume that they weigh less. It just says that they are lightweight.

B. Avian Oculars should be used only by bird watchers.

No such assumption. The argument says that they can be used by birding enthusiasts. Whether someone else also uses them, we don't know.

C. The reader will travel through the habitats of rare species during his or her next bird watching trip.

The advertisement promises the sight of the world's rarest species in all of their beautiful plumage with the use of Avian Oculars. The assumption is that the user will go to habitats of rare species during his or her next trip. Correct.

D. Avian Oculars are similar in cost to traditional binoculars.

It is given in the argument. "Comparable price"

E. Birding enthusiasts often determine the specifications of new products.

The argument does not assume that. It says that Avian Ocular are designed with the features that are demanded by birding enthusiasts. But do birding enthusiasts OFTEN determine specs of new products? We don't know and nor do we care. Our conclusion does not depend on it.

Answer (C)