Question 431873
I and III are the same.

in general, if you have a statement that says: if p, then q, where p and q are some conditions, then this is the same as saying if not q, then not p.

so your question says: If my sister forgets her lines for the play on Friday, then she will not get the part of Juliet. So the "p" part is: the sister forgetting her lines for the play on Friday, and the "q" part is: she will not get the part of Juliet". so now let's rewrite not q, then not p, she will get the part of juliet, then, the sister will not forget her lines for the play on Friday