Answer:
D (ww)
Step-by-step explanation:
This is a cross involving a single gene coding for whisker length in cats. The allele for long whiskers (W) is dominant over the allele for short whiskers (w) i.e. the W allele will mask the expression of w allele in a heterozygous state.
Since long whisker allele (W) is dominant, it means the dominant trait (long whisker) will be expressed if the genotype if a cat is homozygous dominant (WW) or heterozygous (Ww). However, the recessive trait (short whiskers) can only be phenotypically expressed when the cat's genotype is homozygous recessive (ww).
Therefore, if a cross between a Ww (heterozygous) cat and a ww (homozygous recessive) cat produces an offspring with short whiskers, It means that the offspring has a homozygous recessive genotype (ww) since it expresses the recessive trait.