Enzyme isomerase converts glucose-6-phosphate into
fructose-1,6-bisphosphate.
Fructose-6-phosphate
Dihydroxyacetone-phosphate
Glyceraldehyde-3-phosphate.
In the second step of glycolysis, an isomerase converts glucose-6-phosphate into one of its isomers, fructose-6-phosphate.
Hence, the correct option is b.