Which reaction(s) within the Krebs cycle results in the formation of reduced nicotinamide adenine dinucleotide (NADH)?

Conversion of isocitrate to α-ketoglutarate, conversion of α-ketoglutarate to succinyl-CoA, and conversion of malate to oxaloacetate.

Conversion of succinate to fumarate

Conversion of citrate to isocitrate, and conversion of succinate to fumarate

Conversion of citrate to isocitrate, conversion of isocitrate to α-ketoglutarate, and conversion of α-ketoglutarate to succinyl-CoA