In the 1400s, european explorers benefited from
a.
the availability of gps.
b.
the development of time zones.
c.
the use of steam ships.
d.
improvements in map-making skills.

     They benefited from improvements in map-making skills. We know they didn't have GPS. We know time zones has nothing to with it. Have you ever heard of Columbus coming on a steam ship? So D.

D. The improvements in map-making skills. It cant be A cause gps' didnt exist in the 1400s, and steam ships and the time zones werent created until later on in like the 1700s and foward when America was found