Unmatched records are records in one table that have no matching records in a related table

In the accompanying figure, which callout points to the area you should click first when adding a header or footer?

A. D B. G C. C D. A

One of the disadvantages of using 2D codes is:

A) the ease with which a printed code can be stickered over or tampered with. B) that codes are readable without the use of specialized software. C) the unreliability of the transponders used that may run out of power. D) the minimum distance required to read the code.