--Who should be responsible for the accident?-- The boss, not the workers. They just carried out the order .
Scientists have many theories about how the universe_______into being.
Cindy shut the door heavily and burst into tears. No one in the office knew ______she was so angry.
We can never expect_______bluer sky unless we create_______less polluted world.
The visit _____ to Guilin is worth remembering for ever.
Some children want to challenge themselves by learning a language different from their parents speak at home.