When Joe's Gas Raises Its Prices for Regular Unleaded,total Revenue

Multiple Choice

When Joe's Gas raises its prices for regular unleaded,total revenue from both regular unleaded falls to zero.It must be the case that:

A) the demand for Joe's regular unleaded gasoline is perfectly elastic.
B) the demand for regular unleaded must be inelastic.
C) there are NOT many good substitutes for regular unleaded gasoline.
D) consumers are switching to premium grades of gasoline.