农历七月初七是中国传统的“乞巧节”（学习纺织工艺的节日）。它起源于我国古代“牛郎与织女”的美丽传说。导致这一节日形成的根本原因是（   ）

一次心跳就是心脏的一次收缩过程． 

阅读理解
A
    Jennifer and William live in New York．They have a daughter, Emma，but 3-year-old Emma doesn't live with them．She is in California with her grandparents．It is Jennifer's birthday today．Jennifer and William come to a nice restaurant to celebrate (庆祝)．
Waiter：Good evening，how can I help you today?
William：We'd like a table for two, please．
Waiter：This way，please．
Jennifer：Thank you．Can we have a menu(菜单)?·
Waiter：Here you are．My name is Alan．I'm your waiter today．Would you like to hear today's specials?
William：Sure．
Waiter：Well．today's specials are chicken soup and fish and chips(炸鱼薯条)．
Jennifer：OK．I'd like fish and chips．
William：I would like to have pasta （意大利面食）with tomatoes．
Waiter：OK．Would you like to have some salad? Our salads are great．
Jennifer：I'd like a green salad．
Waiter：Very good．Would you like something to drink?
Jennifer：Oh．Water is OK．
William：I would like some orange juice，please．
Waiter：OK．So that's a green salad, fish and chips and water, pasta with tomatoes and orange juice.
Jennifer：Yes，that's right．
根据材料内容选择最佳答案。

根据 $\frac{1}{2}-\frac{1}{3}=\frac{1}{6}$ ， $\frac{1}{3}-\frac{1}{4}=\frac{1}{12}$ ，那么 $\frac{1}{99}$ ﹣ $\frac{1}{100}$ =（  ）

Not only ____ strict with us, but also ____ for us.