题目

There is __________ 8-year-old boy playing__________ Chinese chess with his friend in the classroom. A . A; / B . an; / C . a; the D . an; the 答案：B [s1] 下列不属于抗原的是 A.卡介苗       B．破伤风抗毒素        C.白喉类毒素     D.癌细胞  [s1]22.