Final answer:
The generation-skipping tax is levied on transfers to individuals who are two or more generations below the donor, such as grandchildren, which is why option a. Transfers to grandchildren is the correct answer that triggers GST.
Step-by-step explanation:
The generation-skipping tax (GST) is triggered by the transfer of assets to a person who is two or more generations below the donor, typically the donor's grandchildren or any unrelated person more than 37.5 years younger. In the context of the question provided, transfers to grandchildren would be the correct answer as it would most likely trigger the generation-skipping tax. This is because such transfers effectively 'skip' a generation - the donor's children - which is exactly what the generation-skipping tax is designed to capture and tax. On the other hand, transfers to your own children, siblings, or a spouse are typically not subject to GST as they do not involve skipping a generation.