A semi-continuous operation means: A. the operation is continuous each shift, but stops between shifts B. coffee breaks are allowed for the operator C. a computer is a required part of the machine D. each operation in a sequence is continuous, but subsequent operations in the sequence may be different. E. None of the above

The correct answer is: D. each operation in a sequence is continuous, but subsequent operations in the sequence may be different.

A semi-continuous operation is a type of manufacturing process that is not fully continuous, but does have some continuous elements. In a semi-continuous operation, the workpiece is moved through a series of steps, each of which is performed continuously. However, there may be pauses between steps, or the workpiece may be moved to a different machine for the next step.

Option A is incorrect because it describes a continuous operation. In a continuous operation, the workpiece is moved through the process without interruption.

Option B is incorrect because it is not a requirement for a semi-continuous operation. Coffee breaks are allowed for operators in all types of manufacturing processes.

Option C is incorrect because a computer is not a required part of a semi-continuous operation. Some semi-continuous operations may use computers, but others may not.

Option E is incorrect because it is not a complete list of the possible characteristics of a semi-continuous operation.