题目

I work as a postal letter carrier in Charlotte. One day several years ago, I drove up to a   41  . Christy, the young divorcee (离了婚的人) who lived there, was waiting by the roadside. She said that she had a   42   to tell me.About six months  43   it seemed that I had   44  a letter to her which had her street   45   on it but was addressed to another house with the   46   number on a different street in the neighborhood. She decided to   47   the letter at the correct house.It turned out that the letter had been   48  for Johnson, who happened to be   49�海洋动物质量越大，其叫声越是有力而低沉，即响度较______，音调较____。如图所示的甲、乙两曲线为科考船声呐系统收录的500 kg的海豚和t的蓝鲸叫声的波形图，其中，________(选填“甲”或“乙”)波形是蓝鲸发出的。