In the context of sunflower height inheritance, tall (T) is dominant, and short (t) is recessive. Since short plants express the recessive phenotype, they must have the genotype that includes two recessive alleles.
The only genotype that corresponds to the short phenotype is tt.
Among the options provided, the correct choice that represents the genotype of the short plants is:
D tttt
However, "tttt" is not a standard notation for carrying two recessive alleles. The correct form should simply be tt. Based on the options and the understanding of genotype, it appears that option D might be intended to represent that.