Name the number of headphone class for sr100
{'header': ['Headphone Model', 'Headphone Class', 'Sensitivity (dB)', 'Impedance (Ohms)', 'Driver-matched dB', 'Construction', 'Earpads', 'Termination', 'Succeeded by'], 'page_title': 'Grado Labs', 'section_title': 'Past production', 'caption': 'Past production', 'rows': [['SR40', 'Unknown', '100', '32', 'Unknown', 'Plastic', 'Foam', '1/8" (3.5 mm) plug with 1/4" adaptor', 'iGrado'], ['SR325', 'Prestige', '98', '32', '0.05', 'Aluminum Alloy', 'Bowls', '1/4" (6.5 mm) plug', 'SR325i'], ['HP1000', 'Joseph Grado Signature', 'Unknown', '40', 'Unknown', 'Aluminum Alloy', 'Flats', '1/4" (6.5 mm) plug', 'No Successor'], ['SR100', 'Prestige', 'Unknown', '32', 'Unknown', 'Plastic', 'Flats', '1/4" (6.5 mm) plug', 'SR125'], ['SR200', 'Prestige', 'Unknown', '32', 'Unknown', 'Plastic', 'Flats', '1/4" (6.5 mm) plug', 'SR225']]}