100 points i need help please! its for a test thing!

Which flexible structure that supports the nerve cord and led to the backbone

Which of the following describes a boom period? a. as one population increases, another population decreases. b. as one population increases, the other population also increases. c. as one population decreases, another population increases. d. as one population decreases, another population also decreases

This is so important ugh its 25 points