I dont get why is the correct answer the one circled in green and not the above one, what is the use of the // ( backslash) and /// ? : [enter image description here][1]


  [1]: https://i.stack.imgur.com/FDMZb.png

I dont get why is the correct answer the one circled in green and not the above one, what is the use of the // ( backslash) and /// ? 
