Since her husband died, Mrs. Jackson has lived alone in their big old suburban  house, The house was bought by her husband almost fifty years ago.               For the sake of safety  , her son has tried hard to ask her to sell the house and buy a new and small one in the town , But Mrs. Jackson doesn't like the idea. She says that she has to look after her husband's old house. But recently she often hears stories about unknown people stealing things around here.               That was a cold day before Christmas Eve. Around four o'clock in the afternoon, Mrs. Jackson was enjoying the Christmas music when someone knocked at the door. She heard the sound but didn't move. Another knock. Who could it be? Mrs. Jackson was a bit afraid. She decided not to answer the door but keep waiting.               One minute another minute and yet another minute. Nothing happened and no more knocks , She walked quietly to the door, and listened. She heard nothing but the wind outside. She slowly unfastened the door and peeped   through the crack . She then gave a surprised cry and threw the door wide open! At the door she saw a tall, beautiful Christmas tree! In the tree stood a Christmas card with these words:               Merry Christmas! Your new neighbor Why didn't she move when she heard the knock at the door? Because   _  .
she was enjoying the Christmas music she thought it might be an unknown person it was not her son she hadn't decided to answer the door
Question: Since her husband died, Mrs. Jackson has lived alone in their big old suburban  house, The house was bought by her husband almost fifty years ago.               For the sake of safety  , her son has tried hard to ask her to sell the house and buy a new and small one in the town , But Mrs. Jackson doesn't like the idea. She says that she has to look after her husband's old house. But recently she often hears stories about unknown people stealing things around here.               That was a cold day before Christmas Eve. Around four o'clock in the afternoon, Mrs. Jackson was enjoying the Christmas music when someone knocked at the door. She heard the sound but didn't move. Another knock. Who could it be? Mrs. Jackson was a bit afraid. She decided not to answer the door but keep waiting.               One minute another minute and yet another minute. Nothing happened and no more knocks , She walked quietly to the door, and listened. She heard nothing but the wind outside. She slowly unfastened the door and peeped   through the crack . She then gave a surprised cry and threw the door wide open! At the door she saw a tall, beautiful Christmas tree! In the tree stood a Christmas card with these words:               Merry Christmas! Your new neighbor Why didn't she move when she heard the knock at the door? Because   _  .
A. she was enjoying the Christmas music
B. she thought it might be an unknown person
C. it was not her son
D. she hadn't decided to answer the door
Answer: