the bridge which is being built will be completed next year中的which is可以省略吗,为什么?

语法上应该是可以的,但是语感上说不过去,听着别扭.这句是个选择题the bridgebeing 填空will be completed next year。选项有AbuiltBbeing builtCis being built Dbuilding 选B答案上说是因为bridge和built是被动关系。为什么啊being built 是修饰bridge 的。也就是说可以这样省略喽。。。。。。。。。语法上说得过去。