Final answer:
The correct term for the active and inactive, or spore-forming, stages of bacteria is the b. bacterial lifecycle. This includes the formation of endospores under harsh conditions and returning to vegetative growth when conditions are favorable.
Step-by-step explanation:
The active and inactive, or spore-forming, stages of bacteria together are part of the bacterial life cycle.
Bacteria, during unfavorable environmental conditions, can form endospores which allow them to remain dormant until conditions improve.
On return to favorable conditions, these endospores germinate back into active vegetative cells. The process of sporulation and return to vegetative growth is an essential part of the bacterial life cycle ensuring their survival through extreme conditions.
The term bacterial dual-stage is not commonly used in scientific literature, hence the correct term referring to the active and inactive stages of bacteria, in this case, would be the bacterial lifecycle (option b).