In 1985, Robert Hayes leased real estate to Drab Corporation for 20 years under a triple net lease, making Drab Corporation responsible for all maintenance and improvements to the property. In 1990, Drab Corporation, the lessee, made significant capital improvements of $600,000 to the property. In 2005, Drab decides not to renew the lease and vacates the property. At that time, the value of the improvements is $800,000. Robert Hayes sells the real estate in 2017 for $1,200,000 of which $900,000 is attributable to the improvements. When and in what amount of gross receipts is Robert Hayes taxed on attributable solely to the improvements made by Drab Corporation?

a. In 1990, when improvements are made, in the amount of $600,000.

b. In 2005, when the lease ends, in the amount of $600,000.

c. In 2005, when the lease ends, in the amount of $800,000.

d. In 2017, when the real property is sold, in the amount of $900,000.

e. None of these.