Answer:
option "B" is correct (substance 2)
1. An endoskeleton is the internal support of the structure of an organism like bone, cartilage etc. An exoskeleton is a complex rigid outer covering of an organism which protects the muscles and soft tissues inside like a crab shell. Remember it like 'en' in endoskeleton is to enter so its inside, and 'ex' in exoskeleton is to exit so outside the animal.
2. Bone marrow is a semi-solid tissue which is inside the spongy part of bones. There are different colored bone marrow, and the different ones are just located in different types of bones. Bone marrow is important and helps because it is the primary location where the production of new blood cells occur.
Einstein's theory of special relativity sets of the speed of light, 186,000 miles per second (300 million meters per second). ... The speed of light in a vacuum is 186,282 miles per second (299,792 kilometers per second), and in theory nothing can travel faster than light.
