1.A more conclusive answer about life on Mars,past or present, would give researchers invaluable data about the range of conditions under which a planet can generate the complex chemistry that leads to life.
2.The Bush administration seems bent on satisfying the small but vocal group of Americans who oppose stem cell research under any conditions.
答案
1.【解析】该题考察which引导定语从句的用法。Past or present是插入成分，补充说明life on Mars.which 引导定语从句，修饰conditiona,which在从句中作方式状语，前面加介词under.
【句意】有关火星上过去和现在是否存在生命的更加确凿的答案，将向研究人员提供以下方面的珍贵数据，即行星在什么条件下能够导致最终产生生命的复杂化学反应。
2.【解析】该句为主从复合句。主句是the Bush administration seems bent on satisfying the small but vocal group of Americans,定语从句who oppose stem cell research under any conditions来修饰Americans.
【句意】少数人呼声不断，坚决反对出于任何目的的干细胞研究，布什政府似乎已经屈从于满足这些人了。
1.The road of life is long,but only a few steps are crucial especially during some years_______(当人年轻的时候)
2.April Fool’s Day is that special day of the year______(在这一天你可以捉弄别人)
答案
1.when people are young
【解析】该题考察when 引导定语从句的用法。when 在定语从句中充当时间状语，相当于“in which”
2.when you should play a joke on someone
【解析】该题考察when 引导的定语从句。When只能对that special day of the year这类表示时间的名词进行修饰。