As there is less and less coal and oil, scientists are exploring new ways of making use of ____ energy, such as sunlight, wind and water for power and fuel.
Many people like to talk about generation gaps. I don't think there is ________ in my family though.
I will never know what was on his mind at the time, nor will ________.
When Kerry and Sam met again two years later, each was pleased to see ________.
There is a subway in my hometown, but ________ existed two years ago.
I prefer a house in beautiful surroundings in the countryside to ________ in such a noisy street in Shanghai.