Ir - Not or the opposite of something
dis - Apart or away, a negative or reverse force
un - Not or an opposite force
House is the noun clause in the sentence
I believe the correct answer is B. The modifier "wearing a blue dress" is placed far from the noun which is supposed to modify - Stacey. Such as it is, it could easily be attributed to another noun, the stage. It would seem that the stage was wearing a blue dress, rather than Stacey. This is easily fixable with a comma between "stage" and "wearing".
The C and D sentences are also a little bit awkward, but they don't contain a misplaced modifier.
The answer is A.
swept the floor first, then washed the dishes
