【单选题】

"this" in paragraph 4 probably refers to ______
A．The tusks of male elephants are usually large and heavy.

B．Tusks in good condition are in great demand, and may sell for as high as two thousand dollars or more.
C．Elephants are perhaps the only animals that are hunted for their teeth.
D．An elephant uses its long, pointed tusks as tools for digging in the ground for food.