Premise : Since furniture must be useful, cabinetmakers must exercise their craft with an eye to the practical utility of their product.
Conclusion : cabinetmaking is not art.

A) Some furniture is made to be placed in museums, where it will not be used by anyone. - not a good assumption to conclude that cabinetmaking is not art

B) Some cabinetmakers are more concerned than others with the practical utility of the products they produce. - opposite answer , actually weakens the conclusion

C) Cabinetmakers should be more concerned with the practical utility of their products than they currently are. - Candidate - keep it aside
D) An object is not an art object if its maker pays attention to the object's practical utility. - good assumption , keep it aside
E) Artists are not concerned with the monetary value of their products. - not related

Now take a closer look at Option C & D

C) Cabinetmakers should be more concerned with the practical utility of their products than they currently are.
- It looks like cabinetmakers are already concerned that means some of the furniture is not art which is against the conclusion as conclusion captures all the products that cabinetmakers create. So reject this option

D)An object is not an art object if its maker pays attention to the object's practical utility. - This is your answer.

GREAT RESPONSE! THANKS!