U.S. stock mutual funds added a fourth week to their string of advances, though the gains have been successively weak. The average U.S. diversified stock fund added 0.32% in the latest week, according to Lipper data. The rise followed gains of 4.06%, 2.22% and 1.55% the previous three weeks and lifted the year-to-date gain to 6.32%. Large-cap growth rose the most among diversified stock funds in the latest week, rising 0.66%.