Why the quality of sand deteriorates if the same molding sand is used again and again?

A. Build up of clay and other organic coatings on the molding sand particles B. Presence of foreign and scrap matter like iron particles, feyalite, etc. C. Occurrence of pieces of oil sand D. All of these

A. finish allowance B. contraction allowance C. taper allowance D. camber allowance

A. 70% sand and 30% clay B. 40% sand and 60% clay C. 30% sand and 70% clay D. 60% sand and 40% clay

A. Rough surface B. Blow holes C. hot tears D. Drop