The major body structures and organ systems form during which trimester

correct answer is a. and d.

all matter is made up of atoms

in any element all atoms are the same

elements in a compound are always in a constant ratio: apex

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)]