China’s factory-gate prices contracted in April, falling by the steepest margin in four years, as manufacturers struggled with deflationary pressures from the coronavirus pandemic, which has crimped demand both at home and abroad. The producer-price index dropped by 3.1% from a year earlier in April, compared with a 1.5% fall recorded in March, the National Bureau of Statistics said Tuesday. Prices for crude oil and other commodities collapsed, contributing to the decline in wholesale prices. Economists polled by The…