Brass and bronze are both (alloys,composites,variations,void) of copper because copper is the (main,most dense,most expensive,only) component in brass and bronze.
alloys
main
This problem simply requires you to understand the terms used.
Alloy - A metal made by combining two or more metallic elements.
Brass is an alloy of copper and zinc. The ratio of copper to zinc can range widely with copper ranging from 50% to over 65% and zinc making up most of the remainder.
Bronze is an alloy of copper and tin. The modern ratio is about 88% copper and 12% tin.
