根据短文理解, 从A、B、C、D四个选项中选择最佳答案填空。

    I have been collecting stamps since I was a little kid. I began to collect stamps1I was eight years old. At that time, my mother  2 at an international bank. Every Friday, she 3 home stamps from all the letters she had received during that week. I 4had many pen friends in different countries, and we 5 letters to each other very often. By the 6 I was twelve, I have collected more than l, 000 stamps from fifty different countries! I've7  collecting stamps, but now it's  more  8 . My mother retired(退休) from her job, and my pen friends send me  9 messages instead of letters. The Internet has been very  10  for my stamp collection !