Mr.Li often drives his car to work,but he rides a bike there.
A:usually
B:sometimes
C:always
D:often
读世界部分区域示意略图,
人体的免疫系统可以清除体内的① 衰老细胞 ② 正常白细胞 ③ 正常红细胞 ④ 畸变细胞