1. If you are going to speak in public you should learn how to use hand gestures in public speaking.2. I gave the speaker a hand signal while I was leaving.3. I made a thumbs-up gesture to my son when he reached the finish line.
 hand signal hand sign hand gesture注意: 用 make a hand gesture to somebody 而不是 give a hand gesture to somebody.< >
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 effet, which leads to melting of glaciers, which leads to rising sea levels.