Diamond rings are relatively scarce because:
according to geologists, diamonds are less common than is any other gem-quality stone.
of monopolistic competition.
diamond producers limit the quantity supplied to the market.
the demand for diamonds is so high.

Diamond producer restrict diamond quantity supply to certain limit in market

Explanation:

Diamond is a precious gem stone that used for making jewelry pieces and other related items.It is also used for making diamond ring but there is scarcity of it in market as it is an expensive thing and many people are ready for paying lot of amount for it .Thus, producer of diamond limit its supply quantity in market

Other options are incorrect because diamonds are not less common in market than other gems, demand is not extensively high in market and neither it faces monopolistic competition.

responsibilities im assuming

answer; a biased sample;