Which of the following is a feature of osteoporosis?
a. it is most common in men over 45 years of age
b. it has virtually no effect on blood calcium levels
c. it results from short-term deprivation of dietary calcium
d. it causes significant alterations in the blood levels of parathormone and calcitonin
d. it affects about 30 million people in the u. s.

Option A, It is most common in men over 45 years of age

Explanation:

Osteoporosis is caused when the removal of old bone is higher than the creation of new bone . Bones in our body renew continuously and regularly but when a person ages his/her ability to form new bones reduces. Due to this the overall bone mass reduces leading to weaker and porous bone structure. Normally after the age of 30, the capacity to form bones reduces and by the age of early 50s this problem becomes more serious and leads to Osteoporosis.

Thus, option A is correct

gold i'm pretty sure i might be wrong

answer:

convection currents in the magma drive plate tectonics. heat generated from the radioactive decay of elements deep in the interior of the earth creates magma (molten rock) in the aesthenosphere. the aesthenosphere (70 ~ 250 km) is part of the mantle, the middle sphere of the earth that extends to 2900 km.