The process of impregnation in powder metallurgy technique is best described by which of the following?

• A. After sintering operation of powder metallurgy, rapid cooling is performed to avoid thermal stresses
• B. Low melting point metal is filled in the pores of a sintered powder metallurgy product
• C. Liquid oil or grease is filled in the pores of a sintered powder metallurgy product
• D. During sintering operation of powder metallurgy, rapid heating is performed to avoid sudden produce of high internal pressure due to volatilization of lubricant