The slowdown added to worries about the ability of the world’s second-largest economy to offset low growth elsewhere. The country’s gross domestic product grew at an annual rate of 7.6 percent in the April to June period, down sharply from the 9.5 percent a year earlier, according to government figures released Friday morning. The second-quarter growth rate was half a point below the 8.1 percent for the first three months of this year.