Air bubbles formed on the surface of casting is probably due to________________?
		A.	Improper casting pressure
B.	Improper heating of the investment
C.	Improper angulation of sprue
D.	Improper wetting of the wax pattern by the investment
		A.	Improper casting pressure
B.	Improper heating of the investment
C.	Improper angulation of sprue
D.	Improper wetting of the wax pattern by the investment
		A.	Facilitate venting of the mold
B.	Retard the heating of the investment
C.	Permit expansion of the world
D.	All of the above
		A.	Surface hardness
B.	Strength
C.	Proportion limit
D.	Corrosion resistance
		A.	Increasing the mould metal temperature difference
B.	Increasing the flow of molten metal
C.	Flaring the point of the sprue attachment
D.	All of the above
		A.	Carbon
B.	Molybdenum
C.	Chromium
D.	Nickel
		A.	Silica
B.	Quartz
C.	Cristobolite
D.	Calcium sulphate monohydrate
		A.	Unreliable spring back
B.	low spring back
C.	Minimal spring back
D.	None of the above
		A.	Low weight
B.	Low cost
C.	Low strength
D.	Low melting point
		A.	Paraffin
B.	Carnauba
C.	Gum dammar
D.	Canadelila
		A.	Fibrous
B.	Homogeneous
C.	Inhomogenous
D.	amorphous