41.  Worried about his father being alone, so, he called him once a day after he returned home to New York.

42.  A story in the Bible said that once upon the time, all the human beings would like to build a high tower which may reach up to the sky.

43.  Worried about him being alone, I called him once a day.

44.  Once when I tried to reciting a list of about 15 pages of words, I fell to sleep once per page on average.

45.  As professor Duan once told us, every rumor has its basis.

46.  Once in high school, we absorb the knowledge around us but now, we search for new knowledge in all kinds of resources.

47.  There is a classic joke that goes as follows: "Once a student who had got the highest score in the TOEFL ran into a foreigner.

48.  They loved each other, so Aaron was worried about Clyde being alone and called Clyde once a day after he returned home to New York.

49.  Some words are seldom used, so just by reading maybe you would meet them once a year.

50.  Worried about him being alone, I called him once day.