材料一：

科学家做了下面的实验：把家蝇分成多组，每组再分为A、B两部分，用DDT处理每组的A部分，B部分不接触DDT．处理后选死亡率最低的那一组的B部分饲养繁殖，再把后代分成许多组：每组分成A、B两部分，重复上述实验．这样一代一代选择下去，就可以从B部分选出强抗药性的家蝇。

材料二：

镰刀型细胞贫血症患者在幼年时期会夭折，但在疟疾流行的地区，镰刀型细胞贫血症基因的携带者对疟疾的感染率比正常人低得多．现对A、B两地区进行调查，其中B地区流行疟疾。

回答下列问题：

(Some classmates are talking about their weekend.)

    Linda: I stayed at home and studied over the weekend. I studied for my English test on Saturday. Yesterday I wrote a geography paper. In the evening I talked to my pen pal (笔友) on the phone. What did you do?

Tim: I had a good time. On Saturday morning I played tennis, in the afternoon I went to the beach, and in the evening I went to Nancy's birthday party. On Sunday I went to the mountains with my friends.

Mary: Oh, your weekend was great. But mine was boring. I stayed at home the whole (全)weekend. I cleaned my room and washed my clothes. I even watered the flowers. And only in the evening I watched TV for a short time. Did you go out, Dave?

Dave: No, I didn't. I stayed at home and watched TV on Saturday. Yesterday I watched a movie on TV, Fearless. It was very exciting.

在水平桌面上放置一个底面积为100cm²，质量为为400g的圆筒，筒内装有16cm深的某种液体．弹簧测力计的下端挂着一个底面枳为40cm²、高为8cm的金属柱，当金属柱从液面上方逐渐浸入液体中直到全部浸没时．弹簧测力计的示数F与金属柱浸入液体深度h的关系如图所示．（圆筒厚度忽略不计，筒内液体没有溢出，g=lON/kg）

求：