Multi-select problem: How does the next paragraph end?

How to make a plastic sheet greenhouse
String up a clothesline between two bare trees, tightly, about head-high.
Drape a clear plastic sheet over the clothesline.
A standard 9'x12' size works okay, but for more space the bigger the better.

OPT: (a). Clip it with clothes pins to keep it in place. Spread out the sides like an old army pup-tent and fasten them to the ground with rocks or bricks.; (b). Don't try to use objects covering trees, because they can crack over time. Place the plastic against the tree trunk.; (c). Take a piece of white paper and draw a line on the edge of the sheet with a pencil. This line will act as a " crown " in the greenhouse, and the tree should hang onto the edge in the same manner.; (d). It can be identical to a standard larger, but either size is fine. Measure one tree (if measuring a whole tree) from the bottom to the top and mark that tree.;
(a).