Apply a black inset box shadow with a horizontal and vertical offset of 0 pixels, a blur radius of 50 pixels, and a size of 20 pixels. Which CSS property values achieve this effect?
a. box-shadow: inset 0 0 50px 20px #000000;
b. box-shadow: inset 50px 0 0 20px #000000;
c. box-shadow: inset 0 50px 20px 0 #000000;
d. box-shadow: inset 0 0 20px 50px #000000;