we know that
the diameter of the circle divides the circle into two equal parts
so
FA=FB
CG=GD
in the right triangle EAF
EA is the radius r
EF=3.4
applying Pythagoras Theorem
EA²=EF²+FA²
FA=√(r²-3.4²)
in the right triangle CEG
CE is the radius r
EG=3.4
applying Pythagoras Theorem
CE²=EG²+CG²
CG=√(r²-3.4)
then
FA=CG
Hence
AB=CD
therefore
the answer is AB