ea. vol: illus. by David A. Carter. unpaged. Holt. Apr. 1985. pop-up $7.70. PreS-K The brief text in these pop-up books exists only as a vehicle for the paper engineering. What's at the Beach? has a question, such as ``What's behind the pail?'' on one page and a flap with the answer and an animal under it on the facing page. Several of the animals will not be easy for the intended audience to identify. The crab, lobster and snails involve detailed artwork that obscures their identities. What's in the Cave? is more successful as it uses familiar animals. The title question is answered on the first page with the words ``Let's find out.'' Then, each double-page spread has a flap which conceals an animal and a few words to describe it. A snake hides under a log, a spider in a web, a bird in a nest. The flaps open easily, and the pop-up creates an action performed by the animalunflapping its wings, unfolding its legs, leaping out. In both books, the depictions are more cartoon-like than realistic; the purpose is to entertain rather than inform. Each has a finale of a colorful, elaborate monster that pops out of the fold of the last double-page spread. The monsters as well as the other pop-ups would not survive active circulation in a library, and the books would not add much to story hour. They seem to have been created for the bookstore market, and that's where they belong. Kathleen Odean , San Rafael Pub . Lib ., Calif .