Scientists use radioactive decay to measure half-lives
relative time
time of day
absolute time

eukarya because is is like alche and b is bacteria and d is animals

explanation:

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)]