为证明细菌对植物遗体的分解作用，某小组的同学分别提出了以下四种实验方案．四种方案的共同点是：将同一种树的落叶分成基本相同的甲、乙两组；通过滴加蒸馏水，使树叶保持潮湿．其中设计最科学严谨的是（ ）

short

   We all need to exercise. Doctors say it is good for us. It makes your heart and body strong. It also gives you more energy. And you will feel better yourself. It's best to exercise twice a week. Twenty minutes each time is enough.
   There are many ways to exercise. You can walk, run, play sports, or swim. Many people go to special places to exercise. They are called “fitness centers”. These places have a lot of equitment. Some people buy equitment for their homes. But it is very expensive.Exercising can be fun. Friends can exercise together at fithess center. Or they can play sports together, how do you exercise?

依次填入下列各句横线处的成语，最恰当的一项是（        ）

①医疗质量是关系到病人生命安危的大事，救死扶伤是医务人员________的天职。

②中国传统的严父慈母型的家庭关系，常令父亲们________地承担起教育子女的义务。

③在全国比赛中屡获金奖的我省杂技团，________地承担了这次出国演出任务。