.----Who are those people gathering in front of the building?
-----A group itself the youth volunteers.
A. calling
B. calls
C. called
D. to be called
网友回答
(答案→)A. calling
B. calls
C. called
D. to be called
解析：考查现在分词做定语，句意：--在大楼前聚集的人是谁？--一群自称为青年自愿者的人。说明这个空填定语，A group和call itself是主动关系，用现在分词做定语。选A。