正确的化学实验操作是实验成功和人身安全的重要保证．下列实验操作正确的是（ ） A

时代公司拟得到15%的A股票投资报酬率，A股票目前的价格为39.69元，每年的股利预计以后每年以5%的增长率增长。试问A股票上年每股股利为多少

什么是约定账户还款？

Password is a secret series of (69) that enables a user to access a file, computer, or program. On multi-user systems, each user must enter his or her password before the computer will respond to (70) . The password helps ensure that (71) users do not access the computer. In addition, data files and programs may require a password.

A．power

B．authorized

C．accredit

D．unauthorized

润滑油在机械中的作用有哪些？

半精车外圆时要留0.6mm的磨削余量，对2×45°的导角应导成（）。

A.2×45°

B.2.3×45°

C.2.5×45°

D.3×45°