Question 5
Two plants both look tall. One is TT and the other Tt. How could you tell them apart?
The right answer is the one marked above.
Cross each with a dwarf plant and look at the offspring. The TT plant gives only tall offspring; the Tt plant gives about half dwarf. That is the whole purpose of a test cross.
You cannot read a genotype off a plant by looking at it. The offspring are the only evidence available about the second allele.