U.S. diversified stock funds lost 4.93% on average in the week ended Jan. 7, starting the year by extending their losing streak to a second straight week and the fifth in the past six weeks, according to Lipper Inc. It was their worst loss since a 6.11% plunge in the week ended Feb. 19, 2009. Investors were rattled by a one-two punch — turmoil in China’s markets and rising tensions in the Mideast.