41.   Most consumers have little idea that unseen advertising networks on the Internet track their movements across multiple Web sites.

42.   NASA, using satellite photos, is able to track the movement of what we think of as ash.

43.   Neither man was traveling with a bodyguard at the time he was kidnapped, and Cheung boasted that he was able to track their movements with uncanny precision.

44.   Now he may be among the first to learn how the Hohokam built the Stonehenge-like monument that tracked annual movements of the sun.

45.   Ossei plots to free his mother and tracks the movements of the native slavers.

46.   Other scientists on shore have studied satellite readings to track the movements of elephant seals tagged with tiny radio transmitters.

47.   Researchers are trying to track the movement of sediments that have been polluted by years of industrial runoff.

48.   Scientists at Massachusetts General Hospital used magnetic resonance imaging to track the movement of silicone in the body and then study its interaction with human cells.

49.   Sen. Hillary Clinton, D-N.Y., a supporter of the measure, said access to the database could help track movements of terrorists.

50.   Scientists were anxiously tracking its movements.