Mark is a U$.$S$.$ citizen who has lived in the United States since birth. He owns stock with a fair market value of $$3$ million. His basis in the stock is $$500,000.$ Mark decides to relinquish his U$.$S$.$ citizenship to move to Singapore. What are the U$.$S$.$ tax consequences of this action?

a$.$ Mark will be subject to U$.$S$.$ taxes on his built$-$in gain, and he will be required to remit payment to the U$.$S$.$ government before he can exit the country.

b$.$ Mark will not qualify as a covered expatriate because there is an exception for stock. He will not have any U$.$S$.$ tax liability.

c$.$ Mark will not qualify as a covered expatriate and be subject to the mark$-$to$-$market tax regime upon expatriation.

d$.$ Mark will not qualify as a covered expatriate because the value of his stock is below the required threshold. He will not have any U$.$S$.$ tax liability.