21.
Non-biodegradable pollutants are created by

22.
Respiratory roots are known as

23.
The conversion of a pond to a climax forest community is an example of

24.
Which of the following is a nonrenewable energy resource?

25.
What type of energy is derived from heated groundwater?

26.
All of the following are advantages of dams except

27.
The combustion of waste in the absence of Oxygen is called

28.
Atmospheric humidity is measured by

29.
Freshwater protozoans react to a/an __________ environment by removing water through _______

30.
Which of the following is the poorest conductor of heat?