最古老的促销方式是（）。
A.人员促销
B.活动促销
C.公共关系促销
D.广告促销
参考答案：A
---Hello, can I speak to Robert, please?
---Hold on, please. He_______ in the garage.
A．has worked
B．is working
C．worked
D．will work
造血干细胞(hematopietic stem cell)
