A tank filled with manure, water and unused crop plant residues ...

[piesebel]

A tank filled with manure, water and unused crop plant residues but which minimizes oxygen content could be used to
 
  A) produce biogas.
  B) produce biogas if the oxygen levels were adjusted to very high concentrations.
  C) burn unused parts of crop plants to generate heat for homes.
  D) collect and store carbon dioxide in underground wells.

Question 2

Volcanoes are triggered by
 
  A) changes in solar radiation.
  B) movement of tectonic plates.
  C) human mining activities.
  D) major changes in climate.

[fdliggud]

Answer to Question 1

A

Answer to Question 2

B

[piesebel]

Gracias!

[peter]

Excellent