$1\frac{3}{5}$的分数单位是____，它有____个这样的分数单位．
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根据短文理解，从A、B、C、D四个选项中选择最佳答案填空。

    Mr and Mrs Yates had one daughter.   1   name was Carol, and she was nineteen years old. Carol lived  2 her parents and worked in an office. She had some friends, but she  3any of the boys very much.

    Then she met a very  4 young man. His name was George. and he  5  in a bank near her office. They went out together quite  6 , and he came to Carol’s parents’ house twice, and then last week Carol went to her father and said, “I  7 George, Daddy. ”

    “Oh, yes,” said  8  .“he’s a nice boy. But has he got any money?”

    “Oh, men! All of you are  9  ,” the daughter answered    10  . “I met George on the first of June and on the second he said to me, ‘Has your father got any money?’”

冬小麦在每年秋季播种，次年春末夏初收获。下图是某地区冬小麦生育期（作物从播种到成熟所需的时间）日数图。导致M、N两地冬小麦生育期不同的主要因素是（    ）