1.chemicals -> gases

- Dẫn chứng : They don't use coal or oil , so they don't produce dangerous gases (dòng 2)

2.electricity -> coal and oil 

- Dẫn chứng : They don't use coal or oil , so they don't produce dangerous gases (dòng 2)

3.expensive -> cheap 

- Dẫn chứng : The house was very cheap to build (dòng 4)

4.stone -> wooden 

- Dẫn chứng : It has wooden walls , and floors (dòng 4)

5.on top of -> in the mud

- Dẫn chứng : John and Kathy get water from a well and they grow vegetables in the mud on top of the house