At first it seemed that the building would be all right but later it was found to need ______ which required careful designing.

【正确答案】 B

【答案解析】 installation意为“安装”；modification意为“更改，修改”；innovation意为“革新”；illustration意为“说明”。根据句意“起初这栋建筑看起来似乎都没有问题，但是之后发现它需要作详细的设计修改”可知，B项正确。