Would it be ____for you to pick me up at four o’clock and take me to the airport?

A．free

B．vacant

C．handy

D．convenient

在国际上为了使作为历史资料的重要文件，在长期保存中签署的姓名清晰，则签署文件时一般用                                                                                              

A．蓝墨水

B．碳素墨水

C．蓝黑墨水

D．墨汁