1. The lion picked off the weakest member of the herd.2. We singled him out as our opponent because he is the weakest of his team.
pick offpick off 就是挑一個人或動物下手, 已經有攻擊的意思. single out 只是指挑一個人或動物
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 meltin of glaciers, which leads to rising sea levels.