-- Is this a pen? -- Yes , ________ is.A. this B. that C. it
---Do you know sound travels very fast? ----Yes. But light travels _______ sound.
Paper-making is one of _______ of ancient China.
Could you please give some _______ to the _______ teachers?
Please wait here. I’ll be back in _______ hours.
----Have you found your lost mobile phone? ----No, I haven’t found _______. I have to buy a new _______.