Which of the following is a protein maintained at constant levels throughout the cell cycle that requires cyclin to become catalytically active?
a) pdgf
b) mpf
c) protein kinase
d) cyclin
e) cdk

organ system-an organ system is a group of organs that work together to perform one or more functions. each does a particular job in the body, and is made up of certain tissues.

answer : haversian

[explanation: -(compact bone is organized as parallel columns, known as haversian systems, which run lengthwise down the axis of long bones. these columns are composed of lamellae, concentric rings of bone, surrounding a central channel, or haversian canal, that contains the nerves, blood vessels, and lymphatic system of the bone)]