Instruction: Parse the product information to locate the target attribute, and then provide the extracted value of the target attribute and its source in the output, specifying None if the attribute is not present.

Input:
Product title: Opella 14157 16.1" Round Self Rimming / Undermount Bar Sink, Brushed Stainless
Product description: Outside Diameter: 16.1\". Inside Diameter: 14.1\". Depth: 7\". Material:18 Gauge Stainless Steel. Undermount Or Drop-In. 2-1/2\" Drain Opening. Full manufacturers warranty included
Product feature: Outside Diameter: 16.1", Inside Diameter: 14.1"., Depth 7", Material:18/8.5" Stainless Steel., Undermount Or Drop-In., 2-1/2" Drain Opening, Full manufacturers warranty included
Product price: $4.92
Product brand: Opella
Target attributes: Material
Answer: attribute: material
value: stainless steel
source: product feature
attribute: material
value: stainless
source: product title
attribute: material
value: stainless steel
source: product description