为了减少汽车对大气的污染，1998年6月我国成功地开发出以新燃料做能源的“绿色汽

计算：a²•（ab）³=______．

You need ________ fit.

A．exercise keeping

B．to exercise to keep

C．exercising keeping

D．to exercise keeping

Only by practising constantly__________ greater progress.

A．we can make

B．then we will make

C．can we make

D．we must make

设计和管理中的部分数据，也属于产品数据管理的范畴。( )