The correct answer is B. 'She's'. When making a contraction, take the two words that you want to make into a contraction and replace at least one letter from the second word with an apostrophe.
She has
In this case, these are the words that we're trying to turn into a contraction. There really isn't any way to explain why we use 'She's' instead of 'She'as', except that 'She's' is the commonly accepted word in the English language.
She's
Now, replace the letters 'h' and 'a' with an apostrophe.
Hope this helps!
