short selling

Identify the risk, unique to short selling, that Teri accepts when she chooses to sell short.
A. Need to maintain adequate margin.
B. Use of margin magnifies risk and return.
C. Need to meet new margin calls.
D. Unlimited loss.
老师您好， 这题考的是short selling的risk么？ 正确答案是D， 为什么A不对呢