NEW YORK (AP) — U.S. stocks flipped between minor gains and losses in morning trading Friday. Builders started work on more houses in April, as U.S. construction surged to its highest pace in six months, the Commerce Department announced before the market opened. Almost all of that increase, however, came from new apartment buildings, a sign that Americans are still struggling to buy single-family homes. The stock's jump followed news that Warren Buffett's Berkshire Hathaway revealed a new investment in the telecom late Thursday. Rising sales helped the department store chain turn in better results than analysts expected late Thursday. Sales at stores open at least a year — a key gauge of a chain's health — increased more than 6 percent in its first quarter.