DNA acts as a sort of set of instructions for building an organism.
In that way, different types of organisms--plants, animals, bacteria, etc.--can all be differentiated through their DNA because it is directly linked to how they function.
Segregation of alleles happens when the pair of alleles of each parent separate and only one allele passes from each parent on to an offspring. So if you had heterozygous tall plants and mated them (Tt x Tt), they would each separate into T and t, allowing each offspring to get either a T or a t from each parent. The possible genotypes would be TT, Tt and tt.
I’m pretty sure it’s C if not A