string[][] d = new string[c.Count][];
            for (int i = 0; i < c.Count; i++)
            {
                d[i] = ((ArrayList)c[i]).Cast<string>().ToArray();
            }

------解决方案--------------------
C# code
object[][] temp_arr=c.ToArray().Select(x=>(x as ArrayList).ToArray()).ToArray();

------解决方案--------------------

C# code

            string[][] d = new string[c.Count][];
            for (int i = 0; i < c.Count; i++)
            {
                ArrayList al = (ArrayList)c[i];
                d[i] = new string[al.Count];
                for (int j = 0; j < al.Count; j++)
                    d[i][j] = al[j].ToString();
            }