What is a difference between exoskeletons and endoskeletons?
a. an exoskeleton is rigid, and an endoskeleton is flexible
b. endoskeleton are only found in vertebrates
c. exoskeletons are composed of calcium, and endoskeletons are composedd of chitin
d. exoskeletons are external to the soft tissues, and endoskeletons are internal

d. exoskeletons are external to the soft tissues, and endoskeletons are internal

Explanation:

The skeleton can be define as the body part of the living beings which act as a supporting structure which maintains the posture and provides the supporting framework to the body. The exoskeleton is the skeletal structure that protects the body from outside. It encloses within it the soft tissues and organs of the body. It is the characteristic feature of the invertebrates. It is the external feature of the body. It also provides protection against the predator. The endoskeleton is the skeletal structure which serves as a attachment point for the muscles. It is the internal feature of the body.

thats not a question