---We’ve seen many more days of blue skies recently.
---True. But back in 1998, ________ Beijing started its “Defending the Blue Sky”program, the city only ________ about 100 days a year.　　

1. A.
   which, sees
2. B.
   that, saw
3. C.
   when, saw
4. D.
   and, seeing

---We’ve seen many more days of blue skies recently.

---True. But back in 1998, ________ Beijing started its “Defending the Blue Sky” program, the city only ________ about 100 days a year.

A．which, sees 　      B．that, saw          C．when, saw          D．and, seeing

---We’ve seen many more days of blue skies recently.

　 ---True. But back in 1998, ________ Beijing started its “Defending the Blue Sky”　 　　　　program, the city only ________ about 100 days a year.　　

         A．which, sees 　 B．that, saw           C．when, saw        D．and, seeing