15. Shell molding is best described by which one of the following: (A) casting operation in which the molten metal has been poured out after a thin shell has been solidified in the mold, (B) casting process in which the mold is a thin shell of sand bonded by a thermosetting resin, (C) sand casting operation in which the pattern is a shell rather than a solid form, (D) casting operation used to make artificial sea shells, (E) none of the above?