The Burj Khalifa in Dubai is 828 meters high and there is no doubt it’s the tallest building in the world.
A. that
B. what
C. whether
D. which
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(答案→)A. that
B. what
C. whether
D. which
解析：考察同位语从句。固定句式:There is no doubt that…毫无疑问…；本句中的that是一个同位语从句，介绍前面名词doubt的内容，因为上文是no doubt，说明这是一个确定的事实。故使用that来表示一个确定的事实。句意：迪拜的The Burj Khalifa高达828米，毫无疑问是世界上最高的大楼。故A正确。