documentclass[11pt]{beamer}
usepackage[utf8]{inputenc}
usepackage[T1]{fontenc}
usepackage{lmodern}
usepackage[english]{babel}
usepackage{amsmath}
usepackage{amsfonts}
usepackage{amssymb}
usepackage{graphicx}
usetheme{Berlin}
usepackage{graphics}
usepackage{longtable}

    begin{table}
        begin{center}label{tab:plan}
            begin{scriptsize}
                begin{longtable}{|p{2.8cm}|p{3.9cm}|p{1.4cm}|p{1.8cm}|}
                    hline
                    multicolumn{4}{|c|}{textbf{Timeline and Milestones}}
                    \
                    hline
                    centering textbf{Specific Objectives} & centering
                    textbf{Tasks} & centering textbf{Schedule} &
                    textbf{Milestones}
                    \
                    hline  centering textbf{1.Literature review and preliminary and background
                        work} &
                    begin{itemize}[topsep=0pt]
                        item [a)] Literature review of theory and applications,
                        item [b)] Analysing existing the problems,
                        item [c)] Familiarizing with the various programs
                    end{itemize}&centering Half Term I & Prepare summary literature survey by end of term
                \
                    hline
                      end{longtable}
            end{scriptsize}
        end{center}
end{document}