Which of the following statements about listed property is true?

a$.$ A taxpayer can elect to expense an asset if its business use is greater than $35\%.$

b$.$ A taxpayer must use straight$-$line depreciation if the business use is above $50\%.$

c$.$ Passenger vehicles weighing $6,000$ pounds or less, barring specific exclusions, are considered listed property.

d$.$ If business use drops below $75\%,$ then the prior years' excess depreciation must be added to income.