Answer:
a. Centromere
A centromere is a specialised DNA sequence of a chromosome that links pair of sister chromarids (a dyad)
If you have both parents with long ears and some of the offsprings have short ears, you can say both parents are heterozygous for this. Both have a dominant (long ear), and a recessive allele (short ear).
To prove this, you can draw a Punnett square, and you'll see the probabilities of the offsprings.
