Johnny and Wang Gang are going to plant nine seedlings on the straight roads on both sides of the campus, and every two trees are 4 cm apart. At present, they have a tape measure 10cm long. Please.
The distance between two trees is 4cm, and the tape measure is 10cm, which means that the tape measure can span three trees.
After planting two trees, according to the principle of three points and one line, lean the tape measure against these two trees and straighten the tape measure.