Have been used as a grid measurement system for navigating the earth for hundreds of years.
a. gps systems
b. the stars
c. latitude and longitude
d. compasses

C. Latitude and Longitude  

Explanation:

Latitude is the angle formed between the equator and an estimated point.

All points in Ecuador have geographical latitude equal to 0º. Points north of the equator have latitudes greater than 0º, ranging up to 90º, which is the latitude of the north geographic pole. Likewise, the latitudes south of the terrestrial equator vary from 0º to 90º, latitude of the south geographic pole.

To differentiate the values, a positive signal is assigned to the northern latitudes and negative to the southern latitudes.

Longitude is the angle formed between the given meridian and the Greenwich meridian. Longitude is measured from 0º to 180º, east or west of Greenwich.

By convention, signals are also assigned to the longitudes: negative west and positive east. By having the latitude and longitude values of a desired location, we will have determined its geographic coordinates.

the awnser is a

it is not b or c