Identify the type of chemical reaction in the following statement and define each of them: 

a. Digestion of food in our body. 

b. Rusting of iron. 

c. Heating of manganese dioxide with aluminium powder. 

d. Blue colour of copper sulphate solution disappears when iron filings are added to it. 

e. Dilute hydrochloric acid is added to sodium hydroxide solution to form sodium chloride and water.