China’s economy begins 2018 facing what its own leaders call three years of “critical battles.” Those fights to tackle domestic debt, poverty and pollution pose a hat-trick of risks to the world’s No. 2 economy even before higher interest rates and trade war threats from the U.S. are taken into account. While the nation is starting from a position of strength, with full-year growth in 2017 poised for its first acceleration since 2010, the expansion is seen slowing in 2018.