新研制及经过重大改进的作业工具应由（）鉴定通过，批准后方准使用。

A、铁路局及以上部门

B、铁道部

C、国家质量技术部门

D、安全质量监督部门

Last Sunday I went to visit the History Museum where I saw a pot _________ about 1,000 years before.

A．so it had been

B．so had it been

C．what it had been

D．as it had been