Remove unique values in textfile - if else - Python

I have a text file looking like the following:

A   B   C   D
0   4   3   5
3   3   5   8
8   1   5   7
9   3   7   9

The data is sorted by column C. What I am trying to do, is to write a Python (3.4) that deletes each line, where the value in column C does not equal the value of column C in another line. So I need to pull out all lines, that have one or more matching values of column C. The mockup code below, is my attempt to show what I want to do:

For loop
    if lineXcolumnY == lineX2columnY2
    OR
    if lineX2columnY2 == lineXcolumnY
        print line X
    Else
        Delete line X

On the above example of data, the code would then give me:

A   B   C   D
3   3   5   8
8   1   5   7

I am a complete newbie to Python, so what is confusing me a lot, is how to actually refer to the text file in the script, and how to refer to a specific column. In R I would do Data$C to refer to the column, but in Python?