If you travel to another country, on business or vacation, it is helpful to learn some of the country's customs ________ you don't offend the local people. [ ]

A. in that  

B. so that

C. on condition that  

D. except that

迄今为止在我国发现的面积最大的一座地下宫殿是______，它是西汉第六代楚襄王刘注夫妻的合葬墓。