11.   After some initial glitches, the system has proved popular with commuters.

12.   But Oregon officials think their system has already proved itself.

13.   But others think the system could prove to be unfair.

14.   But the regional system proved too expensive, Wattenmaker said.

15.   Especially important, Faulkner said, the system proved effective in hard-to-diagnose groups such as younger women and women with small tumors.

16.   Even worse, the systems generally proved unreliable.

17.   For many of the older refugees, who grew up under the Soviet state, the American private-enterprise system has proven a cultural shock.

18.   If the system proves workable in the trials, it is expected to begin commercial operations within months.

19.   In fact, the system may prove particularly useful on the ground, and not just for planes.

20.   In particular, too, the traction-control system proved a boon.