Directions: In the following question, two statements are given with some words in bold. Which of the following pairs of bold words must be interchanged to make both sentences grammatically correct?

a. A medical cure(A) suddenly warning(B) doctors to breakthrough(C) a disease that once killed thousands of people.
b. Since the tornado siren(D) was not working, law enforcement officers went from house to house to propagate(E) the storm allowed(F).