I think the correct answer is D
Gravity , Explosion
<u>Explanation:</u>
Nebulae are made of dust and gases—mostly hydrogen and helium. The dust and gases in a nebula are very spread out, but gravity can slowly begin to pull together clumps of dust and gas. As these clumps get bigger and bigger, their gravity gets stronger and stronger.
Eventually, the clump of dust and gas gets so big that it collapses from its own gravity. The collapse causes the material at the center of the cloud to heat up-and this hot core is the beginning of a star.
In my opinion, the correct answer among the choice given above is option D. It is advantageous for grazing mammals to gather in groups because groups <span>offer greater protection from predation. It protects them because predators will think twice in nearing the group because it is outnumbered.</span>
The four phases of the menstrual cycle are menstruation, the follicular phase, ovulation, and the luteal phase. Common menstrual problems include heavy or painful periods and premenstrual syndrome (PMS). Knowing when in the menstrual cycle a woman is most likely to conceive can increase the chance of pregnancy.
