Julia, Kasia, Susanna, and Helena have their birthdays on March $$1^{\rm st}$$, May $$17^{\rm th}$$, July $$20^{\rm th}$$, and March $$20^{\rm th}$$. Kasia and Susanna were born in the same month. Julia and Susanna were born on the same day of a month. Which of the girls was born on May $$17^{\rm th}$$? ． 
Overseas Competition->Knowledge Point->Counting Modules->Permutations and Combinations->Combinations
Susanna: March 20\textsuperscript{th}  Kasia: March 1\textsuperscript{st}  Julia: July 20\textsuperscript{th}  Helena: May 17\textsuperscript{th} 