已知点A的坐标为(a,b)，O为坐标原点，连接OA，将线段OA绕点O按逆时针方向旋转90°得线段$O{A}_1$，则点$A_1$的坐标为（   ）

她是谁？可以说：

读下面的古诗，完成题目。

                                                                                                                                               望岳
                                                                                                                               岱宗夫如何？齐鲁青未了。
                                                                                                                               造化钟神秀，阴阳割昏晓。
                                                                                                                               荡胸生曾云，决眦入归鸟。
                                                                                                                               会当凌绝顶，一览众山小。