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: ASUS U31SG-AS31 13.3-Inch Laptop (Black)
Product description: 13.3" HD (1366x768) / Intel Core i3-2350M (2.3GHz) / 4GB DDR3 / Nvidia GT 610M 1GB / 500GB 5400RPM / Windows 7 Home Premium (64Bit) / 802.11BGN / 0.3MP Camera / Bluetooth 3.0 / 8 Cell Battery / HDMI Port / 1YR Global/1YR Accidental Damage/30-Day Zero Bright Dot/2-way FREE shipping/24-7 tech support
Product feature: Intel 2.3 GHz, 4 GB DIMM, 500 GB 5400 rpm Hard Drive, 13.3-Inch LED Screen, NVIDIA GeForce GT610M Graphics
Product brand: Asus
Target attributes: Refresh Rate
Answer: attribute: refresh rate
value: None
source: None