in the membranous skeleton sheath surrounds the central nervous system I perineural ii perineurium iii peritoneum iv perichondrium

The answer is perineural since peri means around and neural CNS

- Rate of respiration is relatively constant throughout the day. It can be concluded that plants do not rely on sunlight to respire.

- Rate of photosynthesis varies at different times of the day and it occurs at its greatest at noon. It can be concluded that plants rely heavily on sunlight to photosynthesise.

Hope this helps:)