China's factory activity expanded at the fastest pace in a year in March, welcome news for the world's second-largest economy before expected tariffs by the United States that could further strain trade ties. The official manufacturing purchasing managers' index (PMI) was 50.5, versus 50.2 in February, the National Bureau of Statistics said Monday. The median forecast of economists surveyed by Bloomberg was 50.4. Any number above 50 points to expansion.The non-manufacturing measure of activity in the construction and services sectors rose to 50.8 from 50.4 last month.