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.
Answer:
Natural selection causes change in allele frequencies within a population.
So option A is correct one.
Explanation:
Natural selection generally work on an organism’s phenotype, or observable features. Phenotype is often largely a product of genotype (the alleles, or gene versions, the organism carries). When a phenotype produced by certain alleles helps organisms survive and reproduce better than their peers, natural selection can increase the frequency of the helpful alleles from one generation to the next – that is, it can cause microevolution.
Epithelia are classified by the number of cell layers and the general shape of the cells
That statement is not correct for asexual reproduction.
Asexual reproduction is when an organism produces offspring that inherit the same genes of the producer (it's essentially, a copy of itself).
It´s a type of reproduction practiced by Achaea and bacteria which are single-celled organisms.
