教学过程的首要事件是（）
A.引起学生注意
B.提示教学内容
C.唤起先前经验
D.呈现教学内容
参考答案：A
Having checked the doors were closed , and _________ all the lights were off, the boy opened the door to his bedroom.
A．why
B．that
C．when
D．where
腰背痛的病因可分为（）
A.肿瘤性
B.先天性
C.退行性
D.炎症性
E.外伤性
