The answer is E) 0.
If:
A - dominant allele,
a - recessive allele,
then:
AA - dominant homozygous (tall),
aa - recessive homozygous (short),
Aa - heterozygous (tall).
A heterozygous plant (Aa) is crossed with a homozygous tall plant (AA):
Parental generation: Aa x AA
F1 generation: AA AA Aa Aa
All of the offspring is tall (AA or Aa), since tall is dominant to short.
There is no chance for offspring to be short (aa).