—What are you doing?
—I am _________ a letter.[ ]
A. write
B. writing
C. writes
答案:B
血友病是一组遗传性凝血障碍的出血性疾病,下列哪组最多见()
A.血友病甲
B.血友病乙
C.血友病丙
D.血管性假性血友病
E.以上都不是