题目

All my life I had wanted a dog. I had two cats that I adored like children, but I still wanted the company of a dog. Then unfortunately I lost my cats. Soon came another shock that my husband left me forever because of lung cancer. I felt I had just lost everything that ever mattered to me. I voiced these feelings to a friend, who took me to a pet store. The store was holding an adoption day with shelters. I looked at and held several puppies (小狗)，wondering which to choose. Then I met Maggie. She looked at me with the saddest eyes I had ever seen, then laid her head on my should对某电子元件进行使用寿命追踪调查，情况如下，试估计该电子元件使用寿命的平均值．寿命（h）[100，200）[200，300）[300，400）[400，500）[500，600）个数2030804030