随着科学技术和社会的发展，超声波已广泛应用于各个领域．下列事例中，利用超声波传递信息的是（　　）

近日全国各地乐天马特超市关门，是抵制                  事件的做法。（   ）

下列对文章内容的分析，不正确的一项是(    )

若二次根式$\sqrt{x-3}$在实数范围内有意义，则x的取值范围是____.

    Are you able to send a letter with pictures and sounds to someone somewhere in the world without a stamp(邮票) on it? Using a computer you can send e-mails quickly and easily. The post is much slower than e-mail. E-mail can send its message to the other side of the world in seconds.

    E-mail is easy to use and it saves time and money. The differences in time in different parts of the world do not matter when sending e-mail. It's twenty-four-hour service(服务) that you can send e-mail at any time of the day or night. No one has to be there to get e-mail. It does not matter if your friends are in beds when you send e-mail to them, or you are seeing a movie at the movie theater when they send e-mail back.