When it comes to the letter grade on your test or homework, you might notice that there is no letter E. Have you ever thought about why that is so?

    In the A, B, C, D and F grading system, the first four letters are typically considered passing grades. An F in this system simply stands for“fail”.The word“fail”happens to start with the letter F, which seems to leave out the letter E. The fact”．Some schools have U grade for“unsatisfactory”,or I grade for “incomplete”.

    Even with all this said, we should also point out that E grade actually has been used pretty commonly throughout the history of letter grades in the US.

    The first college in the US to use a letter grading system like the ones we use today is Mount Holyoke College. In 1897, they began to use the following grading scale:

A: 95-100%(excellent)       B: 85-94%(good)      C: 76-84%(fair)

D: 75%(barely passed)       E: below 75%(failed)

    We can see the inclusion of E instead of F.

    Gradually,the letter grading system became more popular throughout the US. However, many schools decided to drop the E grade and go straight to F.There is no evidence(证据) to really support this, but one possible explanation is that teachers were worried that some students and parents might mistake E for “excellent”.

    Why do we have letter grades? Well, part of the reason is that they made grading simpler during a time of great change for schools. As the 20th century began,growing cities and an increase in immigration led to larger school classrooms. Most teachers at that time thought this new letter grading system was an easy, fair and clear way to grade students.

    Today, more and more people argue that letter grades don't fully reflect(反映) student learning. However，as teachers try to improve grading methods, many parents continue to favor the letter grades they got as kids, they are familiar(熟悉) and easy for parents to understand. So while they might not be perfect, the letter grades probably aren't going away any time soon.

    Helen Keller was a very bright and beautiful girl. When she was six months old, she could already say a few words. But before she was two years old, a serious illness visited her. She could not see or hear, and soon she could not talk. When she was six, her parents invited a teacher for her. She learned to read books for the blind people. She also learned to swim and ride a horse. After she grew up, she became a famous writer in America. Her first and most famous book is The Story of My Life. Her story has brought hope to many blind and deaf people. It encouraged them to live and work.

    No one wakes up feeling happy every day. Very happy people are not different. They never stop trying to be happy. Here are some of the habits of happy people.

    ◆They slow down.

    Sometimes we think too much. {#blank#}1{#/blank#} Happy people know how to enjoy the taste of their meal, enjoy the world's colors, even just step outside to enjoy fresh air.

    ◆{#blank#}2{#/blank#}

    Getting your body moving for as little as 10minutes can make you happy. Happy people exercise regularly and follow through on it because they know it will help them get in good mood (情绪) and stay in good mood.

    ◆They spend money on other people.

    Research shows that spending money on others makes you much happier than spending it on yourself. This is especially true of small things that show effort, such as going out of your way to buy your friend a book that you know he or she will like.

    ◆They get enough sleep.

    {#blank#}3{#/blank#} Your energy, attention and memory all go down when you don't sleep well. Happy people make sleep a first thing of all.

    ◆They have deep conversations.

    Happy people know that happiness and depth go hand-in-hand. They avoid saying mean things about people. {#blank#}4{#/blank#} They talk with others on a deeper level, because they know doing it feels good and is an interesting way to learn.