Explain six transport modes

Which of the following is not a challenge to instituting sound global environmental policies? a. most changes are inexpensive and easy to implement. b. elected leaders who support unpopular environmental issues often are not re-elected. c. economic considerations outweigh environmental ones in many societies. d. there is no way to enforce international environmental agreements.

What would be the distance of all the planets to the sun in astronomical units?

What first caused people to consider that the continents were once one large landmass?