Multi-choice problem: Continue writing the next sentence in this paragraph:

How to mulch around a tree
Shovel away old mulch, dirt, and rocks.
Shovel away all the old mulch, debris, and rocks so that you can see the tree trunk. A " mulch volcano " occurs when mulch is piled up year after year on the base of a tree.

Pick from: a). Don't touch the tree trunk with any bare fingers because the roots will still be clinging to it and the resulting mulch will rot with time. A mulch volcano promotes a bacterial breeding ground of your tree. b). To fix this, dig around the tree to gather dirt, rocks, snow, or gravel. Use wire stripping when digging around the tree trunk to give it a sturdy surface to pull up and off. c). Mulch piled up at the base of a tree is detrimental and starves the roots of needed oxygen. Cut up-growing roots with pruners. d). You've inflated the trunk a little, putting in weeds and rocks instead of mulch, so your tree is composed of smaller, more compact rocks. Scrub the tree trunk with a garden hose.
c).