The unit of length most suitable for measuring the thickness of a cell phone is a . the unit of length most suitable for measuring the height of a backyard tree is a .

Millimeter and meter

Explanation:

Cellphones are only a few millimeters in thickness.

It is easier to say 5 millimeter than 0.0005 meter.

The unit we use must help others easily visualize and understand the size of the object.

a 5 millimeter is easy to visualize than a 0.0005 meter or a 5,000,000 nano meter

In the same way, a tree in our backyard usually grow as tall as a few meters. ( remember trees in amazon forest might grow as tall as a few kilometers). so in the case of trees in our home the right unit to measure them is meters.

it breaks and dirupture other materials and other sencews from the bottom