If the circle x ^ 2 + y ^ 2 = 1 is translated along the positive direction of X axis and tangent to the line L: X-Y = 0, then the translation vector a is equal to () A.(1,0) B. (radical 2,0) C.(2,0) D. (double root 2,0)

If the circle x ^ 2 + y ^ 2 = 1 is translated along the positive direction of X axis and tangent to the line L: X-Y = 0, then the translation vector a is equal to () A.(1,0) B. (radical 2,0) C.(2,0) D. (double root 2,0)

When it is tangent to the line L: X-Y = 0, the center coordinate of the circle is (root 2,0)
So the translation vector a equals B. (radical 2,0)