Final answer:
The true statement about heterochromatin is 'd) Neither A nor B', as it does not contain most structural genes and is not readily accessible to proteins.
Step-by-step explanation:
The correct answer to the question about heterochromatin is d) Neither A nor B. Heterochromatin is a tightly packaged form of DNA, and it is generally found in regions such as the centromere and telomeres. It usually contains genes that are not actively expressed or transcribed. Therefore, heterochromatin does not contain most structural genes (a) and is not extended and accessible to proteins (b).