单项选择题 In conclusion, walking is a cheap, safe, enjoyable and ______ available form of exercise.

单项选择题 The ______ amongst the world's scientists is that the world is likely to warm up over the next few decades.

单项选择题 After the students were shot by the military during a demonstration against the army ______, the girl students dared for the first time to stay out at night on the streets to picket.