完成句子
Nobody knows for sure ___________________________(这个世界何时形成).
Most teachers rank students _______________________(根据他们的成绩).
He is learning spoken English __________________(以至于)he can work with foreigners.
Nuclear power will __________________ (对……有害) our health and safety if it is not used properly.
Our teachers always __________________ (注意) combining theory with practice.