Final answer:
The candlestick is the correct answer as it is commonly used as an inexpensive decorative household item, while the other options serve different primary functions.
Step-by-step explanation:
An inexpensive object used as a household decoration among the options provided is a) Candlestick. While each item listed could theoretically be a decorative object, candlesticks are commonly used to decorate homes and are often both functional and ornamental. Candlesticks can vary greatly in style and detailing, fitting various decors from modern to traditional. The other options such as keepsakes, knapsacks, and kettlebells have their own uses: keepsakes are items kept for sentimental reasons, knapsacks are bags carried on one's back, and kettlebells are tools for physical exercise. However, it's the candlestick that is typically acquired for the explicit purpose of decorating a household.
The canteen described from the Smithsonian's Freer Gallery, though resembling a household item, is notably different due to its hammered brass and silver inlay and is not intended for practical use. Similarly, the Bauhaus design movement, mentioned in reference to tea kettles, blends functionality with artistic design, indicating that everyday items can indeed be art pieces, as candlesticks often are within a household setting.