Final answer:
To stack two fields in ArcGIS for labeling, use the expression [FieldA] & vbNewLine & [FieldB].
Step-by-step explanation:
The correct expression to stack two fields in ArcGIS for labeling is option C:
[FieldA] & vbNewLine & [FieldB]
This expression uses the & operator to concatenate the values of FieldA and FieldB, and the vbNewLine function to insert a line break between them. Here's an example: If FieldA contains 'First Name' and FieldB contains 'Last Name', the expression would display:
First Name
Last Name