The correct answer is D. machine hours.
Sundry overhead expenses are indirect costs that cannot be easily traced to a specific product or service. They include costs such as rent, utilities, and insurance. These costs are often apportioned, or allocated, to products or services based on some measure of activity. Machine hours is a common measure of activity for apportioning sundry overhead expenses because it is a good indicator of the amount of resources that a product or service uses.
Option A, material consumed, is not a good measure of activity for apportioning sundry overhead expenses because it does not take into account the amount of time or effort that is required to produce a product or service. Option B, number of employees, is also not a good measure of activity because it does not take into account the different skills and levels of experience of employees. Option C, labor hours, is a better measure of activity than material consumed or number of employees, but it is still not as good as machine hours because it does not take into account the different types of machines that are used to produce a product or service.
In conclusion, the correct answer is D. machine hours.