To answer this question, the user needs to know the definition of the term "sprue." A sprue is a passage or channel that allows molten material to flow into a mold during casting.
Now, let's go through each option and explain why it is right or wrong:
A. Outflow: This option is incorrect because a sprue is not a passage for outflow. Instead, it is a passage for inflow of molten material.
B. Smooth flow: This option is incorrect because a sprue is not a passage for smooth flow. It is specifically designed to allow controlled and directed flow of molten material into a mold.
C. Inflow: This option is correct. A sprue is a passage or channel that allows molten material to flow into a mold during casting. Thus, option C is the correct answer.
D. Solidification of the molten material: This option is incorrect because a sprue is not related to the solidification of the molten material. Instead, it is related to the initial introduction of molten material into the mold.
The Answer is: C