I wished to make a round-the-world tour by plane but I hadn't enough money to pay for the ___.

Reducing the gap between the rich and the poor is one of the main ___________meeting the government.

This law which has just been passed is a that the government will pay more attention to protecting wildlife．

 In this research, two are _____, and the others are _____.

 Most air pollution is caused by the burning of _________ like coal, gas and oil.