扫描电子显微镜景深长，成像具有较强的立体感，可用于观察核孔复合体等精细结构。

—Up to now the Chinese Communist Party（中 * * 党）has nearly     history.

—Yes, it was founded       July 23rd, 1921.



A．90 years; at

B．90-year; in

C．90-years; of

D．90-year; on