焊缝表面裂纹在渗透探伤时显示的形状迹痕通常是（）
题型：填空题
问题：
焊缝表面裂纹在渗透探伤时显示的形状迹痕通常是（）
题型：填空题
Thousands of villages in the developing world have no telephones. They have no money to build telephone systems. A new kind of technology may help change this situation. I t reduces the cost of building and using telephone systems.
Traditional systems use wires to carry electrical signals from one telephone to another. The wires often cost much more than telephones. The new system is based on radio communication. Each telephone sends and receives signals through the air, but not through the wires. This reduces the cost greatly. The radio telephone gets their power from the sun.
Each is connected to a solar equipment that changes the sun’s energy into electricity. A battery stores the electricity until someone needs to make or receive a call. The telephone turns off by itself if the level of power in the battery falls too low. This prevents damage to the system. Each radio telephone is connected to a computer microprocessor. It rewards how many calls are sent and received. It controls the power supply.
The technology needs more study, but its new use of radio equipment sun power and computers may help start telephone ringing in the other parts of the world.
68. The radio telephone gets their power from_____.
A. the sun B. electricity C. 
battery D. a special equipment
69. Each telephone is connected to_____.
A. a solar equipment B. a radio machine
C. a computer microprocessor D. Both A and C
70. From the passage we can infer that_____.
A. the new telephone system costs less than before
B. we can not use the radio as before
C. the new telephone system will take the place of the old one
D. it will be much easier to radio from now on
71. The main idea of the passage is_____.
A. a simple telephone system has been invented and
costs less money
B. thousands of villages will use the new telephone system very soon
C. traditional telephone system will become useless
D. the new system will be too good to use