He knew the problem was serious and undertook to look into it       he reached  the office.

A．suddenly

B．immediately

C．abruptly

D．shortly

尚书正式以“台”称，成为国家最高行政机关的独立机构的时期是（）

A.东汉

B.魏晋南北朝

C.曹魏

D.隋朝