At times the balance in nature is ______, resulting in a number of possibly unforeseen effects.
When the students _____ the teacher about their problems, he was ready to give a helping hand.
If you cheat in the exam ,you could hardly ___________ it .
There is a(n) ________ of peace and calm in the country, quite different from that of a big city.
It is reported that Beijing and Zhangjiakou(张家口)will compete to host the 2022 Winter Olympics, which will _____ China’s social development.
With the Internet widely used, a(an)___change has taken place in the way people communicate with one another.