When the ceremony beings, the chairman goes to the stage and gives a welcome speech.
 chairman gives a welcome speech a welcome speech by the chairmanchairman = 儀式或典禮的主席< >
這是一個連環問題: 燃燒石油導致二氧化碳增加，二氧化碳增加導致溫室效應，溫室效應導致冰層融化、海平面上升。 (請填空)
This is a chain of problems. Burning oil leads to increase in carbon dioxide, which leads to the greenhouse effect, which leads to melting of glaciers, which leads to risig sea levels.