Mr. Scott has worked at a police station since he left army five years ago. He's brave and has already caught many thieves. He was promoted   to the rank of officer last month. Now he works harder. It was Mrs. Scott's birthday yesterday. The woman thought her husband was very busy, and she decided to hold a small party only with her husband. Mr. Scott agreed with her and they didn't invite any friends of theirs to the party. At noon he didn't go home for lunch and went to a shop. There he bought an expensive diamond necklace for his wife. He hoped to put it on her neck with his own hands at the party. To his sorrow, a rich woman's house was broken into and some jewelry was stolen, and at once he was sent there to solve the case  ,when he came back to his office, it was late at night. He was tired and hungry. He brought out the necklace and was going to leave when he was asked to answer a telephone. Several minutes later when he came into his office, he found the necklace was gone, and he saw the case   only on his table. He became very angry and called all the policemen in and told them about it. But nobody admitted having stolen the necklace. "I'll give you a chance." Said Mr. Scott, " All the lights will be turned off. The man who took the necklace away will be able to put the necklace into the case in the dark." A few minutes later, Mr. Scott turned on the lights again. To his surprise, the case was also stolen. Mr. Scott was promoted because    _   .
he had been in the army. he was young. he had worked there for five years. he did his duty better than his workmates.
Question: Mr. Scott has worked at a police station since he left army five years ago. He's brave and has already caught many thieves. He was promoted   to the rank of officer last month. Now he works harder. It was Mrs. Scott's birthday yesterday. The woman thought her husband was very busy, and she decided to hold a small party only with her husband. Mr. Scott agreed with her and they didn't invite any friends of theirs to the party. At noon he didn't go home for lunch and went to a shop. There he bought an expensive diamond necklace for his wife. He hoped to put it on her neck with his own hands at the party. To his sorrow, a rich woman's house was broken into and some jewelry was stolen, and at once he was sent there to solve the case  ,when he came back to his office, it was late at night. He was tired and hungry. He brought out the necklace and was going to leave when he was asked to answer a telephone. Several minutes later when he came into his office, he found the necklace was gone, and he saw the case   only on his table. He became very angry and called all the policemen in and told them about it. But nobody admitted having stolen the necklace. "I'll give you a chance." Said Mr. Scott, " All the lights will be turned off. The man who took the necklace away will be able to put the necklace into the case in the dark." A few minutes later, Mr. Scott turned on the lights again. To his surprise, the case was also stolen. Mr. Scott was promoted because    _   .
A. he had been in the army.
B. he was young.
C. he had worked there for five years.
D. he did his duty better than his workmates.
Answer: