Complete the sentences with the correct words and phrases in their proper forms . 选择括号内适当的单词或短语并用其适当形式完成下面的句子。(average, item, product, produce, gas, suppose, breathe, pure, alive, warn, protect, join,replace, hardly, hardly any, exchange) 1. These shirts are 100% ____________ cotton. 2. We don’t know whether he's____________ or dead. 3. Computers won't ____________ teachers in classrooms. 4. The air was so cold that we could hardly ____________. 5. Hydrogen (H2) is a ____________ that easily causes a fire. 6. Why do you ____________ that she is not telling the truth? 7. Please help me ____________ the two pipes together to make a long one. 8. I tried to ____________ him not to get into the trouble, but he didn’t listen. 9. The high-speed train travels at an ____________ speed of 350 kilometres per hour. 10. There's ____________ tea left in the cupboard. Will you buy some on your way back? 11. Mum, do I have to buy all the ____________ on the shopping list from the supermarket? 12. To ____________ more masks for market supply (供应), the company needs more materials. 13. The last day of Christmas (Boxing Day) is a time for family members to ____________ presents. 14. The hi-tech (高科技) company says they will introduce a new ____________ before the end of the year. 15. The fireman felt it was his duty to ____________ the child. He tried his best to save him out of the fire.