The answer is A) An inner skeleton made of bone or cartilage. Vertebrates have a column of bones that supports the body and protects the spinal cord, while invertebrates are animals that either have a soft body or a hard outer casing covering their body.
Uranium-238 is found only in igneous or volcanic rocks. They can date a very ancient fossil also but carbon cannot date and ancient fossil. Trees are not very ancient. Carbon-14 can be used to measure only fossils of recent age.
They are spindle shaped and have no striations.
