We cannot figure out ______ quite a numberof students were infected with the flu.

This returned Chinese scholar has become one of the top experts in this field.—-Yes,I know him very well.He____in Africa with animals for eight years

依次填入下列各句横线处的成语，最恰当的一项是 (　　)①中国古代讲求________，如司马迁把《史记》中所有讳其父的“谈”字都去掉了。②对于群众反映的食品安全问题，相关部门不应回避。如果有关人员________，将失去解决问题的良机。③记者调查发现，不少城市的出租车司机上缴给出租车公司的承包费用很不透明，利益相关方对此________。

ndfather still plays tennis now and then,he’s in his nineties.

_____ is known to us all is that the 2008 Olympic Games will take place in Beijing. [ ]