His Achilles' heel is his absolute loyalty to his friends. One day he may get betrayed by his fair-weather friend.
 Achilles' heel fatal weakness是正統的美語說法.
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 glaiers, which leads to rising sea levels.