Identify the option that includes all the reactions of the Krebs cycle during which oxidative decarboxylation occurs. 

M. oxaloacetate to citrate 

N. citrate to alpha-ketoglutarate 

O. alpha-ketoglutarate to succinyl CoA

P. oxaloacetate to fumarate 

Q. fumarate to malate 

R. malate to oxaloacetate