Were you able to recover your stolen laptop（）

单项选择题It is essential to have an alphabetical index with any numerical system. This involves more work in setting up the system and maintaining it（）.

A．signing
B．marking
C．layering
D．keeping it in good order

单项选择题Whom should a secretary inform before a meeting（） .

A．All those authorized to participate
B．Presents and participants
C．The participants who have titles
D．None