The primary reason for assembly lines in factories is a) less need for overtime work. b) workers learn all parts of the assembly process. c) workers are able to use a wide range of skills in making products. d) workers are able to focus on a specific task in the assembly process.

The correct answer is D. Workers are able to focus on a specific task in the assembly process.

Explanation:

In factories, the use of assembly lines implies in each section of the line or workstation one specific task is completed. For example, in the process of creating toy cars in one workstation, the wheels would be added, then in another, the car would be painted and in other, it would be boxed.

This method of manufacture is often implemented due to its many advantages, one of these is that workers do not need to know about all the process but they just learn and focus on the task they are assigned, and therefore the process is more effective and faster. Thus, one primary reason for assembly lines in factories is "workers are able to focus on a specific task in the assembly process".