翻译下列句子: 1. The welding machine is the power source for arc welding. Without it, we cannot do arc welding. 2. The electrode holder is used to hold the electrode. 3. The electrode is a kind of welding material. It melts in welding. It is used as a filler metal and carries current. 4. The arc produces much heat. It can heat and melt the metal. 5. Workpiece is the metal to be welded. 6. Work clamp is used to connect the workpiece to the welding machine. 7. Electrode cable is used to connect the welding machine to the electrode. 8. Welding machine is a piece of welding equipment. 9. Welding machine can supply the proper amperage and voltage. 10. Welding machine also can convert alternating current into direct current. 11. There are two types of welding machine, AC welding machine and DC welding machine. 12. If the machine supplies alternating current, it is an AC welding machine. 13. If the machine supplies direct current, it is a DC welding machine. 14. Both AC machine and DC machine have two sockets for the cables. One is for the electrode cable. The other is for the work clamp cable. 15. The controls in the machine are used to control the amperage and the voltage. 16. Welding machine can’t generate the electricity. 17. Welding machine gets electricity from outside. 18. Welding machine gets the electricity from the power line or a generator. 19. There is a cable at the back of the welding machine. 20. The cable is connected to the electric box.