A person who has work experience in the U.S. has an advantage or edge in the job market when he comes back to his mother country.
 at an advantage have the advantage of something be welcome everywhere指佔到便宜.
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 effec, which leads to melting of glaciers, which leads to rising sea levels.