观察DNA和RNA在细胞中分布的实验中，下列操作正确的是（    ）

某同学用如甲图所示的电路测定电源的电动势和内阻，所用的实验器材有：待    测电源E，电阻箱R（最大阻值99.99Ω），定值电阻R₀（阻值为2.0Ω），电压表（量程为    3V，内阻约为2kΩ），开关S．

实验步骤：将电阻箱阻值调到最大，先闭合开关S，多次调节电阻箱，记下电压表的示数U和电阻箱相应的阻值R，以 $\frac{1}{U}$ 为纵坐标，R为横坐标，作 $\frac{1}{U}-R$ 图线（如图乙）．

    According to legend, a young man, while wandering the desert, came across a spring of delicious crystal-clear water. The 1 was so sweet, he filled his leather container so he could bring some back to a tribal elder who had been his2.

    After a four-day journey he 3 the water to the old man who took a deep drink, smiled warmly and4 his student lavishly(浪费地) for the sweet water. The young man returned to his with a5 heart.

    Later, the teacher let another student 6 the water. He spat it out, saying it was 7 It apparently had become stale(不新鲜的) because of the old8container. The student 9his teacher: “Master, the water was 10Why did you11to like it?” The teacher replied, “You only tasted the water, I tasted the12The water was simply the container for an get of loving-kindness and 13 could be sweeter.” I think we understand this lesson best when we receive14gifts of love from young children. Whether it's an ugly plate or a bracelet, the natural and proper 15 is appreciation and expressed16because we love the idea within the gift.

    Gratitude doesn't always come 17Unfortunately, most children and many adults 18 only the thing given rather than the feeling embodied(被体现) in it. We should remind ourselves and19our children about the beauty and purity of feelings and expressions of gratitude.20gifts from the heart are really gifts of the heart.

读中国地形图，回答问题。