7. The major cause for variation in air pressure on the Earth's surface
is
A. the variation in specific heat of substances as they are
heated by the sun
B. the rotation of the Earth on its axis
C. the variation in the distance of the Earth from the sun
as it follows its orbit
D. the variation of elevation on the Earth's surface

your a sped   no one cares

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)]

when you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. this increases the space in your chest cavity, into which your lungs expand. the intercostal muscles between your ribs also enlarge the chest cavity. they contract to pull your rib cage both upward and outward when you inhale.