1.Rebel forces in Libya have made a rapid advance westwards against government troops helped by international air strikes which have destroyed many of Colonel Gaddafi's tanks and artillery.
这句话的主干是前面半句。helped by是过去分词作后置定语,修饰Rebel forces。which have destroyed是定语从句,修饰air strikes。
2.But the truth is they would never have made this breakthrough if it hadn't been for the devastating coalition air strikes outside Ajdabiya on Thursday and Friday.
if it hadn't been for虚拟语气
1)表示与现在事实相反的情况,其句型为“ if 主语 动词的过去式( be 动词用 were ),主语 would / could / might / should 动词原形”。如:
If the weather were fine, we would go to Shanghai.
如果天气好,我们就去上海。(事实上天气不好)
If they had time, they would / could / might go with me.
如果他们有时间,他们就会(可能)和我一起去。
2)表示与过去事实相反的情况。其句型为“ if 主语 动词的过去完成式,主语 would / could / should / might have 动词的过去分词”。如:
If I had taken his advice, I shouldn't / wouldn't / couldn't have made such a mistake.
如果我按照他的建议去做,我一定不会(不可能)犯这样的错误。
3)表示与将来事实可能相反的假设和结果,其句型为“ if 主语 动词的过去式 / should 动词原形 / were to 动词原形,主语 would / could / might / should 动词原形”。如: