—Michael, now in hospital, says he regrets drinking and smoking.

—Well, no one knows the value of health            he has lost it.

A．since B．when C．after  D．until

---Michael, now in hospital, says he regrets drinking and smoking．

---Well, no one knows the value of health ________ he has lost it．

1. A.
   since
2. B.
   when
3. C.
   after
4. D.
   until