6．
(1)After that, ________ happened to the Amber Room ________ a mystery.
(2)This was a time ________ the two countries were ________ ________.
(3)He / She only cares about whether the eyewitness has given true information, which must be facts ________ ________ opinions.
(4)There’s ________ much competition among countries to hold the Olympics ________ to win Olympic medals.
(5)Only athletes who have ________ the agreed ________ for their event will be admitted as competitors.