business of the taxpayer if— (i) such property was acquired by the taxpayer by purchase (as defined in section 179(d)(2)) after December 31, 2017, (ii) the original use of such property in the qualified opportunity zone commences with the taxpayer or the taxpayer substantially improves the property, and (iii) during substantially all of the taxpayer’s holding period for such property, substantially all of the use of such property was in a qualified opportunity zone. (B) Substantial improvement For purposes of subparagraph (A)(ii), property shall be treated as substantially improved by the taxpayer only if, during any 30-month period beginning after the date of acquisition of such property, additions to basis with respect to such property in the hands of the taxpayer exceed an amount equal to the adjusted basis of such property at the beginning of such 30-month period in the hands of the taxpayer. (C) Related party For purposes of subparagraph (A)(i), the related person rule of section 179(d)(2) shall be applied pursuant to paragraph (8) of this subsection in lieu of the application of such rule in section 179(d)(2)(A). (5) Qualified opportunity fund The term qualified opportunity fund means any investment vehicle organized as a corporation or a partnership for the purpose of investing in qualified opportunity zone property (other than another qualified opportunity fund) that holds at least 90 percent of its assets in qualified opportunity zone property, determined— (A) on the last day of the first 6-month period of the taxable year of the fund, and (B) on the last day of the taxable year of the fund. (6) Qualified opportunity zone business (A) In general The term qualified opportunity zone business means a trade or business— (i) in which substantially all of the tangible property owned or leased by the taxpayer is qualified opportunity zone business property, (ii) which satisfies the requirements of paragraphs (2), (4), and (8) of section 1397C(b), and (iii) which is not described in section 144(c)(6)(B). (B)