求A。

上午8点30分，时钟的时针和分针所构成的锐角度数为____

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                                                                                     使至塞上
                                                                                        王维
                                                                    单车欲问边，属国过居延。
                                                                    征蓬出汉塞，归雁入胡天。
                                                                    大漠孤烟直，长河落日圆。
                                                                    萧关逢候骑，都护在燕然。