8. He was so deep in thought, thinking of the problem ______ he knocked into the tree without noticing it.
—How’s your tour around the North Lake? Is it beautiful?—It _______ be, but it is now heavily polluted.
All the other boys have geography books and they will be ahead of me if I don’t get ______.
There is ______ small temple on the island, which can only be reached by ______ water.
—How did you find your visit to the exhibition, John? —______
So, ________ the government has a good system of control or can educate the people, the forests will slowly disappear.