衣着素净（   ）

要使两物体间的万有引力减小到原来的 $\frac{1}{4}$ ，下列办法可采用的是（　　）

    A few years ago, my young sons, Sam, Jerry and Alex, joined a bike competition in a town far from our home. As their father was busy, I drove them to the competition.

    We were quite new to the town and didn't know anyone there. But soon after arriving, one woman gave me a chair. In the afternoon, we talked happily. Her name was Bev and she was there with her sons Jim and Carl.

    Unluckily, in one of the last races, my youngest son, Alex, had an accident (事故). He cried and cried, so I ran to meet him. He badly broke his arm.

    Just before I decided to take Alex to hospital, I saw a familiar (熟悉的) face. It was Bev.

    Although I hardly still knew her, she could see I was scared by the accident and the worry of having two other children to care in an unfamiliar town.

    "You go with him to the hospital," Bev said. "I'll take the other two home with my boys. Here is my phone number. I live not far from the town hospital."

    Bev was an angel (天使). I will never forget her kindness in taking two children off my hands so I could give my injured (受伤的) child the best care.

    A friendship started that day; and is still growing now.

-- It's useful for the deaf people to learn sign language.

-- Yes, it's a major way of          for them.