Real Property Income of Foreign Persons

T, a nonresident alien, is a shareholder of X Corp., whose assets consist of a retailing business in Canada and stock of Y Corp. Y's principal asset is an office building in Miami, but is also holds a portfolio of stocks and bonds of Canadian corporations. How might § 897 apply to gain recognized by T on a sale of her X Stock if, alternately:

X holds 40 percent of Y's stock, and alternatively:
X and Y are both domestic corporations?
X is a domestic corporation, and Y is a foreign corporation?
X is a foreign corporation, and Y is a domestic corporation? See Reg. §1.897-2(e)(1).
X holds 60 percent of Y's stock, and alternatively:
X and Y are both domestic corporations?
X is a domestic corporation, and Y is a foreign corporation?
X is a foreign corporation, and Y is a domestic corporation?