30. --- Mrs. Smith, please teach me how to draw on the computer today. 

--- Oh, no._______. You have to get familiar with the keyboard first.

A．It is never too old to learn

B．Think twice before you do

C．Learn to walk before you run

D．One today is worth two tomorrows

根据国标GB/T7714-2005规定，下面的横线上的信息是对（）参考文献的著录条目描述。萧钰.出版业信息化迈入快车道[EB/OL].（2001-12-19）[2002-04-15］.http：∥www.„.htm.

A、标准文献

B、期刊（杂志）

C、电子文献

D、会议文献