You can get seed from a head of cabbage if you grow it yourself. It is a biennial vegetable so it will grow the head the first year and if you leave it in the ground over the winter it will sprout seed heads the next year. You can buy seeds to plant or you can also find seedlings to transplant at garden centers.
Copper and bronze do not contain any iron, and only iron can rust (because rust is defined as iron oxide, a compound of iron and oxygen); so the answer is that steel will rust the fastest and copper and bronze will never 'rust'. But, yes, copper and bronze do tarnish, they do corrode.
(Any metal that is made of iron or steel will rust, metals like copper and silver will simply tarnish.) Students can revisit the examples of metal displayed at the beginning of the lesson and determine which metals will rust, which ones will tarnish, and support their answers with information from the text.