this is one of the experiments___at the moment in our library.

问题描述:

this is one of the experiments___at the moment in our library.
a.being carried b.carried c.carrying d.to carry

选B
首先,carry和experiments是动宾关系,所以要用被动语态,排除C和D
其次,A选项being carried 用的是现在分词短语作定语,一般表示状态,或者是正在进行的动作;而B是过去分词短语作后置定语,与A的区别是,一般表示已经完成的动作.
因此这里选B是最合适的.