单项选择题
In most cases, you can transplant a tree successfully, at any time, if you follow the instructions for planting a tree. The most important thing is to dig out enough roots, but this process is difficult with a large tree.
When you dig out the tree, leave a ball of earth around its roots. This ball of earth should measure about a foot wide for every inch of the tree trunk’s diameter. Dig deep enough to avoid cutting off too many taproots.
It is wise to call in a professional tree expert to transplant a tree more than a few inches in trunk diameter.
A．the heaviest roots
B．the principal, deepest roots
C．the ball of earth
D．the same width as the trunk’s diameter