该句子的主干是voices now come from many quarters；句首Just as结构做比较状语，意为"正如...一样"；insisting 引导的分词结构做定语修饰主语voice，分词结构中含有两个并列的由that引导的宾语从句，第二个宾语从句的真实主语是不定式结构to keep... 翻译：就象吸烟问题一样，来自不同领域的声音坚持认为有关全球变暖的科学资料还不完整。

Just as on smoking, voices now come from many quarters insisting that the science about global warming is incomplete, that it's Ok to keep pouring fumes into the air until we know for sure。

youdao

分析：主语：Americans；谓语：say；that引导一个宾语从句，还包含有一个省略了关联代词的定语从句，a person can be sure in life修饰two things. 当先行词在定语从句中作宾语时，常可省略。

Americans often say that there are only two things a person can be sure of in life: death and taxes.(*)

youdao

本句是并列句，前一个分句中，“if”引导条件状语从句，主句主语“it”指代“the tradition of ambition”。 后一个分句中“who”引导一个定语从句修饰“people”，“the educated not least among them”是“people”的补语。

If the tradition of ambition is to have vitality, it must be widely shared; and it especially must be highly regarded by people who are themselves admired, the educated not least among them。

youdao