The Purchase class contains a ReadOnly property named Tax. The property is associated with the Private _dblTax variable. A button’s Click event procedure instantiates a Purchase object and assigns it to the currentSale variable. Which of the following is valid in the Click event procedure?

a. lblTax.Text = currentSale.Tax.ToString("C2")

b. currentSale.Tax = 15

c. currentSale.Tax = dblPrice * 0.05

d. All of the above