Instruction: Given the title, description, feature, price, and brand of a product and a set of target attributes, extract the value of each target attribute from the product information. Output the extracted value and the corresponding source (e.g., title or feature) denoting where the value is extracted.

Input:
Product title: KEF iQ10BL Bookshelf Speaker (Pair, Black) (Discontinued by Manufacturer)
Product description: Enjoy premium audio with KEF iQ10BL bookshelf speakers, even in areas where space is at a premium. By placing each speaker's 0.75 inch tweeter at the acoustic center of the 5.25 inch midrange driver, the KEF iQ10BL bookshelf speaker pair is able to deliver an expansive audio soundstage. Transitions between high frequencies sound more natural, midrange tones are more refreshing, and hefty, and the extended bass is clean and smooth.
Product feature: 2-way bass reflex speaker, 130-millimeter (5.25-inch) Uni-Q driver, 19-millimeter (0.75-inch) aluminum dome tweeter, Reflex-ported cabinet, Features KEF's "tangerine" waveguide for smoother, clearer high frequency response, Sold as a pair
Product brand: KEF
Target attributes: Configuration
Answer: attribute: configuration
value: speaker pair
source: product description
attribute: configuration
value: 2-way
source: product feature