Global positioning systems (GPS) can "know" their location by
A. measuring the time required for radio signals from four or more satellites to reach the receiver.
B. continually measuring changes in angle to a stationary reference point, such as a streetlight, in the area of the receiver.
C. relating changes in detected radiation to changes in the position of the Sun.
D. relating slight changes in magnetism and gravity to changes in the distance and direction of movement from the point at which the location of the receiver was last calibrated.
Answer: A
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