More and more residences, businesses, and even government agencies are using telephone answering machines to take messages or give information or instructions. Sometimes these machines give (1) instructions, or play messages that are difficult to understand. If you (2) telephone calls, you need to be ready to respond when you get a (3)
The most common machine is the (4) used in residence. If you call a home (5) there is a telephone answering machine (6) you will hear several rings and then a recorded message that (7) says something like this: "Hello. We can’t come to the (8) right now. If you want us to call you back, please leave your name and number after the beep." Then you will hear a "beep", (9) is a brief, high-pitched (10) . After the beep, you can say who you are, whom you want to speak to, and what number the person should call to (11) you, or you can leave a (12) . Some telephone answering machines record for only 20 or 30 seconds after the beep, (13) you must respond quickly.
Some large businesses and government agencies are using telephone answering machines to provide information on (14) about which they receive a large volume of (15) . Generally speaking, using these systems (16) you to have a touch-tone phone ( a phone with buttons rather than a rotary dial). The voice on the machine will tell you to (17) a certain button on your telephone if you want information on Topic A, another button for Topic B, and so on. You listen (18) you hear the topic you want to learn about, and then you push the (19) button. Immediately after making your (20) , you will hear a recorded message on the topic.
3（）
A．that
B．who
C．what
D．which
缺损，
面可见银汞充填物。
为活髓牙。