The correct option is C as big
The given sentence needs to be filled with the most suitable adjective. Looking at 'as yours' we can understand that the sentence is about a comparison between the size of houses and is in the positive degree. 'As' states equality here, which means both the houses are of the same size. Hence we can say 'as big as'. Thus the correct option is B - 'My house is as big as yours.' Option A is incorrect as we need 'as big as' to show the comparison. Option C is incorrect, as 'bigger' is the comparative adjective, whereas 'as big as' is used here to show the comparison. 'Bigger' can be used if someone's house was bigger than others. Option D is incorrect, as 'biggest' is the superlative adjective. Also, 'biggest as' doesn't make sense.