Introduction:
In the context of mechanical engineering, there are various types of tools and machines that are used for different applications. One classification of these machines is based on the relative motion between the tool and the workpiece. In this scenario, the question is asking about the specific type of motion where the tool is stationary and the work reciprocates. Let's explore the different options and understand why option 'A' is the correct answer.

Explanation:

a) Tool is stationary and work reciprocates:
In this configuration, the tool remains fixed in one position while the workpiece moves back and forth in a reciprocating motion. This type of motion is commonly observed in various machines and tools such as shapers, planers, and broaching machines.

b) Work is stationary and tool reciprocates:
In this configuration, the workpiece is held stationary while the tool moves back and forth in a reciprocating motion. This type of motion is often seen in machines such as reciprocating saws or jigsaws, where the cutting tool moves in a reciprocating motion while the workpiece remains fixed.

c) Tool moves over stationary work:
In this configuration, the tool is in motion while the workpiece is held stationary. This type of motion is commonly observed in machines such as milling machines or lathes, where the cutting tool moves over the stationary workpiece to shape or remove material.

d) Tool moves over reciprocating work:
In this configuration, both the tool and the workpiece are in motion. The tool moves over the workpiece that is also undergoing a reciprocating motion. This type of motion is often seen in machines such as surface grinders, where the grinding wheel moves over the reciprocating workpiece to achieve a desired surface finish.

Conclusion:
After analyzing the different options, it is evident that the correct answer is option 'A' where the tool is stationary and the work reciprocates. This type of motion is commonly observed in machines such as planers, where the workpiece moves back and forth while the cutting tool remains fixed.