You can have as many "correct" answers as you wish. You just have to type in the possibilities as "Accept as correct" when you're making the exercise. See the screenshot below - though I'm on a Mac where the layout looks a bit different and the Short answer question is called "Text" but it functions just the same.
I find, however that there's an inherent problem with this type of question: I, and my students, keep finding possible correct answers which I haven't forseen.
PS: By the way, "back yard" written with a space in the middle is not correct as a compound word in my dialect of English. Sometimes the space can even change the meaning: a "black bird" is not the same as a "blackbird". But that's just me being a picky English teacher - not relevant to how Hot Potatoes works.