What is 1, 2, 3 represents in the following flow chart in production of sulfur?

• A. 1-steam, 2-H2S, 3-SO2
• B. 1-H2S, 2-steam, 3-SO2
• C. 1-steam, 2-SO2, 3-H2S
• D. 1-SO2, 2-H2S, 3-steam