题目

△ABC中,已知lga-lgc=lgsinB=-lg,且B为锐角,试判断△ABC的形状. 答案：解:由lgsinB=-lg=lg,可得sinB=,又B为锐角,∴B=45°.由lga-lgc=-lg,得=,∴c=a.又b2=a2+c2-2accosB,∴b2=a2+2a2-a2×=a2.∴a=b，即A=B.又B=45°，∴△ABC为等腰直角三角形. The speaker ________ at the audience and then began to make his speech． [　　] A． glared B． stared C． glanced D． looked