Answer: A TT plant and a Tt plant are both tall.
Explanation: T represents the allele for tall height and t represents the allele for short height. T is written in upper case therefore T is dominant while t is written in lower case therefore t is recessive. A dominant allele will be able to express itself phenotypically, that is, it will be able to show its observable trait in an organism even in the presence of a recessive allele. Since T is dominant, TT and Tt will both manifest as tall because T will be able to mask the outward effect of t.