Which of these are essential non-metallic minerals?
A. Coal, silica, clay, cement
B. Iron, copper, aluminium, zinc
C. Gold, platinum, silver
D. Granite, limestone, marble
Answer:A
Which of these are essential non-metallic minerals?
A. Coal, silica, clay, cement B. Iron, copper, aluminium, zinc C. Gold, platinum, silver D. Granite, limestone, marble