Which of the following best describes $$stack and roll$?$

Question $16$ options:

a$)$

Creates long$-$term hedges from short$-$term futures contracts

b$)$

Can avoid losses on futures contracts by entering into further futures contracts

c$)$

Involves buying a futures contract with one maturity and selling a futures contract with a different maturity

d$)$

Involves two different exposures simultaneously