Directional selection can be distinguished from disruptive selection by .the elimination of extreme variations of traitsb. selection for two extreme variations of a traitc. the preservation of gene frequenciesd. selection for one extreme variation of a trait  i know the correct answer isn't a 

The correct answer is option d, that is, selection for one extreme variation of a trait.  

Directional selection, in population genetics, refers to a medium of natural selection in which an extreme phenotype is preferred over other phenotypes, leading to the shifting of the frequency of an allele in the direction of that phenotype with time.  

On the other hand, disruptive selection illustrates the modifications in population genetics in which the extreme values for a trait are preferred over the intermediate values.  

The answer is option D.

Explanation:

Directional choice, in populace hereditary qualities, alludes to a medium of normal choice in which an extraordinary phenotype is favored over different phenotype, prompting the moving of the recurrence of an allele toward that phenotype with time.  Then again, troublesome determination delineates the alterations in populace hereditary qualities in which the extraordinary qualities for a characteristic are favored over the middle of the road esteems.

step 1 ammonium can be absorbed by plants, but some is converted into nitrates which are better for plants to absorb. this is called nitrification. 2. step 2 the deer eats the plants and uses the nitrogen-containing proteins for cell growth. 3. step 3 bacteria in the soil conduct nitrogen fixation to convert nitrogen gas from the atmosphere into ammonium. 4. step 4 some of the nitrates are absorbed back into plants, but denitrification breaks down the nitrates into nitrogen gas released back into the atmosphere. 5. step 5 nitrogen is found in the urine, which gets broken down into ammonium through the process of ammonification. 6. step 6 plants absorb the ammonium and begin assimilation, the process to add the nitrogen to protein.