许多性传播疾病可经胎盘、产道等途径由母亲传给胎儿,这种传播途径称为
A.血液传播
B.医源性传播
C.日常生活接触传播
D.母婴传播
E.性接触传播
参考答案:D
— What is he doing?
— He ____ back to class. [ ]
A. runing
B. running
C. is running
简述碳化塔启车操作过程?