Can someone explain what is incorrect about C?
C) as those whose
A report shows that there are more than three times as many X and as Y
X = Households where...
Y = [Those = households] whose.....
you've actually pointed out the error yourself!
remember that you have to read extremely literally
if you read this choice extremely literally, it says that households have grandparents (i.e., the households THEMSELVES - not the people in them - have grandparents).
this is absurd.
note that you must ALWAYS read with an extremely literal bent.
this will preclude many expressions that are commonplace in spoken language. for instance, it's incorrect to write that "an author was published twice in the last year", because authors themselves are not published. (you would have to say that the author's work
was published twice in the last year.)