A. Global Positioning Satellite (GPS) and two-way radio
B. The chronometer and the astrolab
C. The cross-staff and the compass.
D. The chronometer and the compass.|||Both radio and GPS were invented before 1999, and that counts as part of the 1900s, so I say A.|||D|||GPS wasnt invented til the 1990s
The compas was around for centuries before 1900.
the only answer left is B, even though i have no idea what an astrolab is|||A.|||B. because both of these instruments were implemented greatly in the 1900's while the cross staff was common in the 1600's and compass has been around since who knows when.
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