Concept:
The midpoint of a line segment joining two points
\[
(x_1,y_1)
\]
and
\[
(x_2,y_2)
\]
is given by
\[
\left(
\frac{x_1+x_2}{2},
\frac{y_1+y_2}{2}
\right).
\]
If a point coincides with the midpoint, then it divides the segment into two equal parts. Consequently, the ratio of division is \(1:1\).
Step 1: Identify the endpoints.
The given endpoints are
\[
(1,2)
\]
and
\[
(5,6).
\]
Step 2: Calculate the midpoint.
Using the midpoint formula,
\[
\left(
\frac{1+5}{2},
\frac{2+6}{2}
\right).
\]
\[
=
\left(
\frac6{2},
\frac8{2}
\right).
\]
\[
=
(3,4).
\]
Step 3: Compare with the given point.
The given point is
\[
(3,4).
\]
The calculated midpoint is also
\[
(3,4).
\]
Hence the given point is exactly the midpoint.
Step 4: Interpret geometrically.
Since the point is the midpoint, it divides the line segment into two equal lengths.
Therefore the ratio of division is
\[
1:1.
\]
Step 5: Verification.
Distance from \((1,2)\) to \((3,4)\) equals
\[
\sqrt{(2)^2+(2)^2}.
\]
Distance from \((3,4)\) to \((5,6)\) is also
\[
\sqrt{(2)^2+(2)^2}.
\]
Hence both segments are equal.
Step 6: Final Conclusion.
\[
\boxed{1:1}
\]
Hence the correct answer is
\[
\boxed{\text{Option (A)}}.
\]