C.asked for
tom是一个能说会道的人么?-不,他从来都不说话除非（有人）叫他说话.
asked for 的意思是有人要求.
如果给题干后再加一个something,那还是要选C．
asked for 是一个常用的词组.
可以给你举几个例子：
the children are very well-behaved and never talked until asked for.
she always minds her own business and never gives her opinion unless asked for.