13. A riser in casting is best described by which of the following:
(A) an insert in the casting that inhibits buoyancy of the core,
(B) gating system in which the sprue feeds directly into the cavity,
(C) metal that is part of the casting,
(D) source of molten metal to feed the casting and compensate for shrinkage during solidification, and
(E) not a waste metal that is usually recycled?
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