Apple Inc’s (AAPL.O) stock was heading toward its first five-session losing streak since January on Thursday as investors worried about the economic health of China, a key market for iPhones. Apple shares were down 2 percent at $120.15 in afternoon trade and have lost about 4 percent since July 1. In the first three months of the year, for the first time, Apple sold more iPhones in China than in the United States, a trend expected to grow as Chinese consumers upgrade from less expensive handsets.