It appears to me that the only change you are making to each string in memo[] is to add a a tab after ')' Could the solution be this simple:
private string data = @"1) Ibrahim was one of the ____ men.
A) wise
B) more wise
C) wiser
D) wisest";
data = data.Replace(") ", ")\t");
Not that simple ? You can use a StringBuilder to reduce the number of strings created:
private string[] splitString = new string[] {")", Environment.NewLine};
string const insertText = ")\t";
var splitdata = data.Split(splitString, StringSplitOptions.RemoveEmptyEntries);
StringBuilder sb = new StringBuilder();
for (int i = 0; i < splitdata.Length; i += 2)
{
sb.AppendLine(splitdata[i] + insertText + splitdata[i + 1]);
}
string processeddata = sb.ToString();