It took me quite a long time to get to the school. It was _______ journey.
A:three hour
B:a three-hours
C:a three-hour
D:three hours
(Ⅰ)求证:平面ABE⊥平面EOD;
(Ⅱ)求平面ECD与平面ABE所成的锐二面角的大小.
极地地区都是冰雪覆盖的寒冷世界,最根本的原因是 ( )
下列词语中没有错别字的一项是( )
—________