Questions

‘Suppose’ and ‘if’ both are used to guess, or think, or imagine something and both means the same thing. So, using them together is superfluous. So, ‘if’will be used. 

Geothermal energy is heat energy generated and stored in the Earth. Geothermal energy has been used for thousands of years in some countries for cooking and heating. It is simply power derived from the Earth's internal heat.

Crop rotation is the technique of planting crops in a different area of the garden so that no single crop will be planted in the same place two—or more—years in a row.

Crop rotation helps to maintain soil structure and nutrient levels and to prevent soilborne pests from getting a foothold in the garden.