题目

I wandered into the small store where I usually buy milk, when the store owner received a call from a customer. The customer and his wife had shopped there several months earlier. He noticed that his wife really liked one thing in the store, so he wanted to buy it as a surprise. But the customer was in Tennessee, far away from the store which was in Maine. What’s more, he had been to the store several months earlier, and it was difficult to believe that the store owner would remember him, or what he was looking for. The store owner took a few close-up photos with her camera, and e-mai燃煤发电厂利用反应2SO2+2CaCO3+X=2CaSO4+2CO2来减少SO2的排放，其中X的化学式为A. O2 B. CO C. CO2 D. H2