go with ashish on the 1st one - C.
But the 2nd one methinks it shud be E.
A - missing they
B - instead of would find a miracle it shud be would have found miraculous
C - not clear abt what the gparents would find miraculous - the household work or the appliances.

D - could is wrong usage, as the sentence is in present tense.
rjtsonu, can u plz post the ans to the previous Qs? dankyu!