In a plant, red fruit (R) is dominant over yellow fruit (r) and tallness (T) is dominant over shortness (t). If a plant with RRTT genotype is crossed with a plant that is rrtt, what will be the phenotype of the offspring?

In the given case, red fruit (R) is dominant over yellow fruit (r) and tallness (T) is dominant over shortness (t). A cross between RRTT and rrtt would result in all offspring having the RrTt genotype. Since R and T are dominant alleles, all offspring will exhibit both dominant phenotypes: tallness and red fruit. So, the correct answer is 'All of the offspring will be tall with red fruits'.