Write the next sentence in this paragraph:

How to make a hamster playpen
Build the walls of the playpen with something slippery.
A playpen needs to be a safe place for your hamster to explore, so it shouldn't be made of materials a hamster can climb or chew. Corrugated plastic is a great option as it is not only slippery, it can easily be cut to any size you need.

A. Another great option is a large rubbermaid-type container with tall sides. You can attach pieces of plastic together with anything from binder clips to duct tape.; B. Attach a tube the size and shape of your pet's snout. Leave enough room for your animal to explore, but not so much that you can cover it entirely.; C. Use construction paper to cut a large rectangle around the perimeter of the playpen. Use a pencil, or a marker to mark both the top and bottom sides.; D. Wood mulch does the same for cardboard. It also helps for insects such as cockroaches and mice.;
A.