Which of the following is a true statement about depreciation on listed property?

a$.$ If listed property is used less than $50$ percent for business purposes, depreciation must be straight$-$line.

b$.$ Listed property includes school buses and tractors.

c$.$ Cellphones and computers generally both meet the definition of listed property.

d$.$ All listed property is not depreciable, and any costs are recovered when the property is sold.