Combine Array Elements in C#

Question

I have an array of string which is

   string[] myarr = new[] { "a", "b", "c" };

Can you please help me how to get this result?

a
ab
abc

I tried this one but I just don't know how to get the value from the array and add it on my list

string[] myarray = new string[] { "a", "b", "c" };
List resultarray = new List();
int i, j;
for (i = 0; i <= myarray.Length; i++)
{
for (j = i; j <= i; j++)
{
}
}