One can’t do extreme sports _________ he or she has had some training.
A．if B．unless C．once D．since
--David, are you 1istening to me?
--Sorry, Dad. I _______ to make sense of what the reporter said.
A．was trying B．have tried C．am trying D．tried
The road construction is based on the agreement, one of _______ purposes is to ensure its completion on time.
A．which B．whose C．that D．what
Many approaches have been _______ to control the spread of H7N9 Bird Flu.
A．adapted B．employed C．negotiated D．accessed
–Carla _______ go to that historical museum after school when she was a teenager.
--No wonder she is so familiar with it.
A．could B．should C．might D．would
It is unfair that one can enjoy _______ just because he or she is rich or powerful.
A．privilege B．possession C．principle D．position
