Which one of the following best defines attributes as used in AutoCAD and defined by the command DDATTDEF?

 attribute is text that can be attached to a block that conveys more information then just the geometry on its own could convey 

so answer no b

this command can link to a data base "A"

(b) Special text entities within a block.

Same as others. My answer is choice (b) Special text entities within a block.

The command "ddatte" and "ddattdef" found in Autocad, which allows the text in blocks to be editable. 

Therefore B) is the answer

Displays a dialogue box that allows creation of an attribute definition for textual information to be associated with a block definition I Controls attribute visibility C Controls Constant/variable mode V Controls verify mode P Controls preset mode

so answer B:

b) Text entities that use an alternative font.

best defines attributes as used in AutoCAD and defined by the command DDATTDEF

(b) Special text entities within a block