Direct proof of continental drift was made possible with measurements of with . a. altitude, lasers b. location, sextants and chronographs c. location, global positioning systems [GPS] d. altitude, global positioning systems [GPS]

c. location, global positioning systems [GPS]

Explanation:

Global positioning system allows the exact location of a place to be noted and pinpointed, hence if there is shift in position of a landmass due to continental drift, the GPS position of that place will change accordingly. This is really helpful in studying continental drifting.