Two circles touch each other externally at C and AB is a common tangent to the circle. Then, ∠ACB is - दो वृत्त एक दूसरे को वाह्यतः C पर स्पर्श करते है और A B वृत्त की एक उभयनिष्ठ स्पर्श रेखा है।∠ACB है-

For two circles touching externally at C with common tangent AB, draw radii from centers to points of tangency. The radii to tangent points are perpendicular to AB. This creates two right angles. The triangle formed is such that ∠ACB = 90° because the radii to C are collinear (since circles touch at C), making the angle subtended by AB at C equal to 90° by tangent properties. Options B, C, D are incorrect.