你知道因为没有医生的处方买不到哪种药吗（　　）

A．风油精

B．红药水

C．板蓝根冲剂

D．链霉素

---Do you know ______?

---Sorry, but if he _____ back, I ____ you know as soon as possible.  

A．when will he be back, comes, will let

B．when he will be back, will come, will let

C．what time will he be back, will come, let

D．what time he will be back, comes, will let