---What happened to the house ?
---It burnt to the ground.
A is said to having been B. is supposed to have been
C is reported to have been D. is believed to have
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解析：句意：--这个房子怎么了？--据报道它已经被烧为灰烬了。这里是Sb/sth is reported/believed/said to do(have done)的结构，因为报道的时候 已经是被烧为灰烬，所以用不定式的完成式，而且是被动式，选C。