Write the next sentence in the following story.

How to build a concrete pool
Mark out and excavate the area of the yard to install the concrete pool.
The hole should be dug approximately 9 to 12 inches (23 to 31 cm) deeper than you want the depth of your pool, to allow room for surfacing the bottom of the basin. A lip is also left around the perimeter of the hole to accommodate sufficient working room for placing forms.

Choose from:
(a). Install plumbing, using pvc pipe and strong bonding material. Your plumbing should include a drain at the bottom of the pool as well as the necessary structure to ensure safe water flow throughout the pool.
(b). Post posts, sliding rails, and poles work well to secure the wooden frames. Plaster mesh works well to supplement the space needed.
(c). Run your hands over the edge of the foundation to ensure that it is level and level. Post and brace edging is the intended purpose of the gravel tub.
(d). A reasonable amount of cement will be made of concrete that is water-based. Collect the concrete according to its package, refilling occasionally to maintain drainage and cracks during the digging process.. The answer should be
(a).