% Author: Prof. Dr. Matthias Jung, DL9MJ
% Year: 2024
\begin{circuitikz}
    \draw(0,0)            node[anchor=south](x1){a.}
        to [open] ++(1,0) node[anchor=south](x2){b.}
        to [open] ++(1,0) node[anchor=south](x3){c.}
        to [open] ++(1,0) node[anchor=south](x4){d.};
    \draw(x1) to [C] ++(0,-1);
    \draw(x2) to [ecapacitor] ++(0,-1);
    \draw(x3) to [variable capacitor,invert, tunable end arrow={Triangle}] ++(0,-1);
    \draw(x4) to [variable capacitor,invert, tunable end arrow={Bar}] ++(0,-1);
\end{circuitikz}