A plane intersects a right circular cylinder of radius $1$ forming an ellipse.  If the major axis of the ellipse of $50\%$ longer than the minor axis, the length of the major axis is

$ \textbf{(A)}\ 1\qquad\textbf{(B)}\ \frac{3}{2}\qquad\textbf{(C)}\ 2\qquad\textbf{(D)}\ \frac{9}{4}\qquad\textbf{(E)}\ 3$
1. Consider a right circular cylinder with radius \( r = 1 \). The diameter of the base of the cylinder is \( 2r = 2 \).

2. When a plane intersects the cylinder, the resulting intersection is an ellipse. The minor axis of this ellipse is equal to the diameter of the base of the cylinder, which is \( 2 \).

3. According to the problem, the major axis of the ellipse is \( 50\% \) longer than the minor axis. Therefore, if the minor axis is \( 2 \), the major axis is \( 2 + 0.5 \times 2 = 2 + 1 = 3 \).

4. Thus, the length of the major axis of the ellipse is \( 3 \).

\[
\boxed{3}
\]