专升本考试

【单选题】 Before you can hear a message on the telephone using the new system, ______.
A．electrical signals must first be changed' into light signals and then into sound
B．the light signals have to be changed directly into sound
C．light must first be changed into electrical signals and then into sound
D．neither the light nor the electrical signals have to be changed in any way

网考网参考答案：C
网考网解析：
从第二段“When the light reaches the other end，…sound message”一句中，可以判断C正确。 查看试题解析出处>>