已知半径为1的动圆与圆（x-5）²+（y+7）²=16相切，则动圆圆心的轨迹方程是______．

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A: 1.      _ are you going on your holiday?

B: I'm 2._    _ to visit Kunming.

A: 3.      _ are you going to get there?

B: By 4.         .

A: 5.                                       ?                  

B: I'm going to the Stone Forest and eat good food.

A: 6.                                       ?

B: I'm going on August 7th.

A: Is Kunming 7.       _ 8.____ Beijing?

B: Yes. It's three hours 9.   ___ plane.

A: 10.                                      there?

B: It's sunny and warm.