latex - 在乳胶中使用子图时，数字不在中心

Question

我用乳胶上下排列两个图形。但是尽管我定义了 \centering，但它们并不位于中心。这是我的代码：

\begin{figure}[htbp]
    \centering
    \subfigure[]
    {
      \begin{minipage}{4cm}
        \centering 
        \includegraphics[scale=0.3]{Figure1-0a.png}
      \end{minipage}
    }

    \subfigure[]
    {
        \begin{minipage}{4cm}
            \centering 
            \includegraphics[scale=0.4]{Figure1-0b.png}
        \end{minipage}
    }
    \caption{Negative effect from wind turbine. (a): harmful to birds (Source: https://arstechnica.com/science/2020/08/black-paint-on-wind-turbines-helps-prevent-bird-massacres/). (b): noise level (Source: https://www.letsgosolar.com/consumer-education/solar-power-wind-power/).} 
    \label{img1-0}
\end{figure}

它显示这样

谁能帮我解决这个问题？