the greens getting ready for their trip

a,the greens特指一个家庭,用复数,b排除
d是现在完成进行时,指过去的动作持续到现在,将来可能进行,d排除
c,can be则是能保持某种状态故排除

A 集合名词表复数的情况，指格林全家所有人

A

2011 years of universiade held in shenzhen, this is a very exciting news. During the universiade in, we can't run and jump, we should walk softly. In the library, should be quiet reading, should not be loud. I hope in the universiade, people during should have good manners.
希望对你有帮助。