Final answer:
The correct unit of measure for the given density of a pine log with a radius of 5 inches and a length of 20 inches is C. lbs/ft³.
Step-by-step explanation:
The student is asking about the density of a pine log, which can be expressed in different units of measure. Density is defined as mass per unit volume. Pine has a different density than other materials like oak or balsa. When logs float in water with a portion above the surface, it indicates a lower density than water, enabling it to float.
The correct unit of measure for the density of the pine log in question, given the radius of 5 inches and a length of 20 inches, and a density of 42.63, is C. lbs/ft³. This unit is consistent with the customary system often used in the United States for such measurements.