Final answer:
The appropriate word to complete the sentence is 'valuable' because the referenced text indicates that the dishes in the china cabinet are of high monetary and possibly sentimental worth.
Step-by-step explanation:
The best word to describe the dishes in the statement "Mom seldom used the _____ antique dishes in the china cabinet," based on the information given, would be C) Valuable. The provided reference indicates that the dishes are of high monetary value, with sentences like "Five thousand dollars, what does that amount to?" and "that punch-bowl alone was worth a fortune." This suggests that the dishes are much more than just expensive; they have considerable worth, potentially both in terms of money and sentimentality.