how to vertically top align a slide in beamer?

Question

The following beamer slide (and all other slides) have the text vertically centered. How do I get it to appear at the top of the slide?

      \documentclass[sansserif,mathserif]{beamer}

      \begin{document}

      \begin{frame}{centered frame}
      centered text, how to get it to top?
      \end{frame}

      \end{document}

Answer 1

\begin{frame}[t]

Frame contents

\end{frame}

does the job

Answer 2

To get this option globally

\documentclass[t]{beamer}

\begin{document}

\begin{frame}
    Text on top
\end{frame}

\end{document}