4. Half of the square of 4.AB is equal to the square of radius-the square of the distance from the center of the circle to the straight line. When AB is equal to the X axis, the distance from the center of the circle to the straight line is the largest, equal to 1, so the minimum value of AB is two threes, so B is chosen.

5. Because the circle is tangent to the X axis, the ordinate of the center of the circle is equal to the radius, that is, 1. Let the center of the circle be (m, 1), and the distance from the center to the straight line can be 4x-3y=0, that is 4m-3=5, so the solution is m=2, so B is chosen.

6. Given that the center of the circle is (-1, 1) and the symmetry point of the line is (2, -2), choose B.

7. It is known that the radius of a circle is 4/2=2 and the center of the circle is on the straight line x+y=0. It is known that the center of the circle is in the fourth quadrant, and only B satisfies the condition.