background
concept
conservation
crisis
drilling
earth
ecology
effect
efficiency
efficient
electric
electrical
electricity
energy
environment
environmental
fuel
gas
global
globe
green
greenhouse
hand
human
industrial
industry
isolated
natural
no
not
notice
oil
people
person
petroleum
planet
pollution
power
resource
save
saving
shortage
sign
stop
symbol
technology
warning
water
white
world