Read the passage and answer the question that follows by choosing the correct option.

I do not know how it is that I have kept the following story so long untold. It is one of the curious things that stop in the bag from which Memory draws out stories haphazardly, like numbers in a lottery. There are plenty of tales just as strange and just as well hidden still left; but some day, you may be sure their turn will come.

One day my charwoman, a working man's wife, came to beg me to honor her sister's wedding with my presence. If you are to realize what this wedding was like, you must know that I paid my charwoman, poor creature, four francs a month; for which sum she came every morning to make my bed, clean my shoes, brush my clothes, sweep the room, and make ready my breakfast, before going to her day's work of turning the handle of a machine, at which hard drudgery she earned five-pence. Her husband, a cabinet maker, made four francs a day at his trade; but as they had three children, it was all that they could do to gain an honest living. Yet I have never met with more sterling honesty than in this man and wife. For five years after I left the quarter, Mere Vaillant used to come on my birthday with a bunch of flowers and some oranges for me-she who had never a sixpence to put by! Want had drawn us together. I never could give her more than a ten-franc piece, and often I had to borrow the money for the occasion. This will perhaps explain my promise to go to the wedding; I hoped to efface myself in these poor people's merry-making.

The charwoman invited the author to attend:

her sister's wedding

These lines from the passage gives the answer of the above question "One day my charwoman, a working man's wife, came to beg me to honor her sister's wedding with my presence."