根据短文理解，从所给的A、B、C、D四个选项中选择最佳答案填空。
Mr. Read works in a big shop. He's very 1 and always gets to the office on time. The 2 is satisfied with (对……满意) him and pays him more. One evening he was very tired, and as soon as he had 3, he put his watch on the table and went to bed. Little Mable, one of his daughters, came in and 4 something there. She dropped the watch to the floor. She picked it up and 5quickly. The next morning he got up on time. After breakfast he had a look at his watch and began to 6 newspapers. When he got to his office, it was half past eight. He was 7 for the first time! At that moment he found something was wrong with his watch. He had to ask someone to 8 it. This morning Mr. Read was going to take a train to London. But he 9 it because his watch was slow again. He was very surprised and said, "It was all right yesterday, but why is it 10 now?" "Last night I found it was dirty," said Little Mable. "I had to wash it for you!"
四种元素原子的最外层电子数之和为20。下列判断正确的是（ ）