Irwin is semi-retired, but he still makes key management decisions for his hardware business. He is involved in several activities, both passive and not passive. All of the following are passive activities except:

a) Trade activity in which he does not materially participate during the tax year

b) Business activity in which he does not materially participate during the tax year

c) Rental activity in which he materially participates but not as a real estate professional

d) Business activity in which he experiences a loss