(19) Laurie Driver.http://commons.wikimedia.org/wiki/Image:
Zebra_mussel_infestation_Ormond_Lock.jpg. Public Domain US Army USACE.
(20) http://commons.wikimedia.org/wiki/Image:Wildfiretopanga.jpg. Public
Domain.
(21) http://en.wikipedia.org/wiki/Image:Available_Energy-2.jpg. Public Domain.
(22) Wagner Christian.http://commons.wikimedia.org/wiki/Image:Windenergy.jpg.
CC-BY-SA-2.5.
(23) Jami Dwyer.http://commons.wikimedia.org/wiki/Image:Lacanja_burn.jpg.
Public Domain.
(24) http://commons.wikimedia.org/wiki/File:
Brown_tree_snake_Boiga_irregularis_2_USGS_Photograph.jpg. Public
Domain-USGOV-INTERIOR-NPS.
(25) Mila Zinkova.http://commons.wikimedia.org/wiki/Image:Oiled_bird_3.jpg.
CC-BY-SA.
(26) User SG.http://commons.wikimedia.org/wiki/Image:
Energy-consumption-per-capita-2003.png. GFDL.
(27) User Willow.http://commons.wikimedia.org/wiki/Image:Salix_alba_008.jpg.
CC_BY-SA.2.5.
(28) Alessandro Cai.http://commons.wikimedia.org/wiki/Image:
Rain_Forest_of_El_Yunque,_Puerto_Rico.jpg. Public Domain.
(29) User HolgerK.http://en.wikipedia.org/wiki/File:Stagnogley.JPG. Public
Domain.
(30) Damien Farrell.
http://commons.wikimedia.org/wiki/Image:Harare_secondst.jpg.
GFDL/CC-BY-SA.
(31) http://commons.wikimedia.org/wiki/File:
Turtle_entangled_in_marinedebris(ghost_net).jpg. Public Domain.
(32) http://commons.wikimedia.org/wiki/Image:Usine_Bret_MG_1643.jpg. Creative
Commons Attribution ShareAlike 2.0 France.
(33) http://commons.wikimedia.org/wiki/Image:Air-pollution.jpg. GNU-FDL.
(34) James Watt.http://commons.wikimedia.org/wiki/Image:
Nwhi_-_French_Frigate_Shoalsreef-_many_fish.jpg. Public Domain US.