Skeletons of early vertebrates were composed of cartilage instead of bone. which characteristic does cartilage share with notochords?

a. it is hard and rigid.

b. it is soft and flexible.

c. it contracts.

d. oxygen can diffuse through it.

The correct answer is option B. It is soft and flexible.

Just like notochord, cartilage is quite soft and flexible. Cartilage serves the purpose of bones in the initial stages of life. Infants have many parts of their bodies which are made up of cartilage instead of bones. These parts are soft  & flexible not hard. Later on because of increased calcification, they transform to become hard bones. One such example is skull. In infants, skull is made up of cartilage and later on it becomes bone which is extremely hard and not at all flexible.  As far as notochord is concerned, it is also made up of cartilage. It is a rod like structure which serves the purpose of spinal cord in all embryonic stages of chordates. In some of the organisms, it still persists in adulthood even after the completion of all embryonic stages.