_______ their service, the workers of the hotel are active in learning English.

In my opinion，life in the twenty－first century is much easier than ________.

Principal White has been working in the school for about 20 years, ____all his energy to teaching and researching as well as the running of a healthy school. 

China’s first aircraft carrier, ____ as long as 304 metres, was handed over to the People’s Liberation Army navy in 2012.

She let the children ______ to play instead of staying at home all the time.