The correct answer is option A and C i.e. Magma and erosion products
The magma is considered as a new product as it is formed from the lava that flows out of the volcano and is a new material produced periodically while the erosion products may not be produced at a particular place but since they are being carried away from some distant area they are new for the area where they are carried to.
This reaction gives the Starch and H2O as the reactants and Maltose as the product.
Amylase is an enzyme which helps in the digestion of Starch molecules and its activity can however be measured through careful monitoring of the disappearance of amylase substrate which is in this case, starch.