示例
通过下面这个例子，并结合以上句子的扩展，体验一下英文句子的各个成分及结构。
But science does provide us with the best available guide to the future, and it is critical that our nation and the world base important policies on the best judgments that science can provide concerning the future consequences of present actions.
解析：
并列句。第一个分句主干：science does provide us。其中with the best available guide to the future为状语修饰provide，the best available和to the future分别为guide的前置定语和后置定语，由此本句宾语被复杂化; 第二个分句主干：it is critical that...,其中，it为形式主语，that从句为真正的主语，从句主语为名词短语our nation and the world, base...on...为固定搭配，第二个that从句为judgments的定语从句，分词结构concerning...为judgments的后置定语。
