SINGAPORE, April 17 (Reuters) – The most active zinc contract on the Shanghai Futures Exchange (ShFE) slipped to its lowest in three weeks on Wednesday, tracking a decline in London markets. The zinc contract in Shanghai was down 1.8 percent at 21,845 yuan ($3,255.69) a tonne, as of 0206 GMT, after slipping to 21,715 yuan a tonne earlier in the session, while the benchmark zinc in London rebounded 0.5 percent. Benchmark zinc ended 3.1 percent weaker in the previous session, its biggest daily fall since August, as a big inflow into the London Metal Exchange (LME) warehouses fanned expectations that a supply deficit would soon end. “Zinc was under pressure for the second day in a row after another surge in inventories on the