What is the primary visible color of an emission nebula? a. red due to ionized hydrogen atoms b. blue due to ionized helium atoms c. red because of reddening by dust d. black, because of dust e. blue from the scattering of light off the tiny molecules

Answer is A. Red due to ionized hydrogen atoms.

Explanation:

Note that nebula color depends on its chemical composition and its degree of ionization. Because of the prevalence of hydrogen and relative low of ionization energy, its emission appears red.

"menstrual cycle is a complex cycle that consists of several processes. order of occurrence of steps in menstrual cycle are as follows:

1. high progesterone levels maintain the endometrium lining of the uterus.

2. endometrium lining breaks down and low levels of estrogen stimulate the pituitary to release fsh and lh.

3. fsh and lh stimulates the follicles to develop and the oocyte to produce estrogen.

4. rising estrogen levels suppress fsh production and development of other follicles.

5. a spike in lh causes follicle to rupture.

6. a breakdown of corpus luteum causes progesterone level to drop."