问题

(2014·济南市名校第四次诊断性测试)—Is the letter from your mother?—Yes.But she ________the letter herself,because she doesn’t even know one word.
A:needn’t have written
B:can’t have written
C:might not have written
D:should not have written
B:can’t have written
C:might not have written
D:should not have written
正确答案是: