下列（）“发小苗而不发老苗”，又称轻土。
A.黏土
B.壤土
C.砂土
参考答案：C
_____ do the students do after-school activities every day ?
For more than one hour.[ ]
A. How often
B. How many
C. How much
D. How long
下图提示心脏的病变为（）
A．左心室肥大
B．房性早搏
C．交界性早搏
D．室性早搏
E．心房颤动
