1.(2019·全国卷Ⅱ，67)I work not because I have to, ________ because I want to.
答案：but not ... but ... “不是……而是……”。
2．(2019· 天津高考，13)Tom is so independent that he never asks his parents' opinion ________ he wants their support.
答案：unless 根据语境可知，这里用从属连词unless引导条件状语从句。
3．(2018·天津高考，4)Let's not pick these peaches until this weekend ________ they get sweet enough to be eaten.
答案：so that 句意：到本周末我们再采摘这些桃子，这样吃起来才够甜。表示“为了，以便”，用so that。
4．(2018·北京高考，2)________ we don't stop climate change, many animals and plants in the world will be gone.
答案：If 句意：如果我们不阻止气候变化，世界上的许多动植物将会消失。表示条件，用If。
