Answer: Option A
The cell address $A4 in a formula means it is a mixed cell reference.
In Microsoft Excel, cell references can be specified in three ways: absolute, relative, and mixed.

• Absolute Cell Reference: A cell reference with a dollar sign ($) before both the column and row identifiers. For example, $A$1. When a formula with an absolute cell reference is copied to another cell, the reference remains the same.
• Relative Cell Reference: A cell reference without any dollar signs. For example, A1. When a formula with a relative cell reference is copied to another cell, the reference changes based on the relative position of the cells.
• Mixed Cell Reference: A cell reference with a dollar sign before either the column or the row identifier, but not both. For example, $A1 or A$1. When a formula with a mixed cell reference is copied to another cell, one part of the reference remains constant while the other changes based on the relative position of the cells.

In the given cell address $A4, the dollar sign ($) appears before the column identifier A but not before the row identifier 4. This indicates that the column reference is fixed while the row reference is relative. So, when the formula is copied to another row, the row reference will change, but the column reference will remain the same.
Therefore, the answer is option A, mixed cell reference.
To summarize, we identified the different types of cell references in Excel and explained that the given cell address is a mixed cell reference because it has a fixed column reference and a relative row reference.