Concept:
The horizontal component of Earth's magnetic field is related to the total magnetic field by
\[
B_H = B\cos\delta,
\]
where
\[
B=\text{total magnetic field},
\]
and
\[
\delta=\text{angle of dip}.
\]
Step 1: Use the given ratio.
Given,
\[
\frac{B}{B_H}=2.
\]
Substituting
\[
B_H=B\cos\delta,
\]
we get
\[
\frac{B}{B\cos\delta}=2.
\]
\[
\frac{1}{\cos\delta}=2.
\]
\[
\cos\delta=\frac{1}{2}.
\]
Step 2: Find the angle of dip.
\[
\delta=\cos^{-1}\left(\frac12\right).
\]
\[
\delta=60^\circ.
\]
Step 3: Write the final answer.
\[
\boxed{\delta=60^\circ}
\]
\[
\boxed{\text{Answer = (C)}}
\]