Write the next sentence in the following story.

How to control the spread of bamboo
Dig a trench around the bamboo.
Dig a trench that is 28 inches (71 cm) deep. The trench should be at least 2 feet (61 cm) away from the bamboo shoot.

Pick from:
I. Walk forward to the trench and dig back with the shovel. Pay attention to where you can go in advance.;
II. Add an extra 3 inches (7.6 cm) to determine how deep you should dig. If you planted bamboo on a smaller patch of grass, you'll have a larger trench.;
III. Make sure that the trench has drainage holes; do not dig deeper than this, or you may rot the bamboo. Water the area, and cover it with a thick layer of bags before you dig it, so that water does not soak through the bags.;
IV. Once the trench is dug, you should be able to locate the bamboo rhizomes growing horizontally under the ground. The rhizomes will look like the main stalk of bamboo growing out of the ground.;. The answer should be
IV.