The Bent Pyramid outside Cairo                  to be ancient Egypt’s first attempt                  a smooth-sided pyramid.

has been believed; to have built

was believed; to build

is believed; to build

is believed; to be built

考查固定短语和非谓语动词。句意：开罗城外的弯曲金字塔被认为是古埃及第一次尝试建造一个光滑的金字塔。第一空为短语be believed to do sth. 表示 “被认为是”，陈述事实为一般现在时的被动语态；第二空名词attempt由序数词first修饰，后跟不定式作后置定语。故选C。