The correct answer you are looking for is A hope it helps
Chambers testified before the HUAC against Hiss and claiming that Hiss belonged to an underground communist organization.
should be " testified " and " claimed "....so their both past tense
"All of a sudden..." is a transition that shows suspense. It says something happened, but it didn't happen with any warning and it doesn't tell the reader up front what went on or if it was good or bad.
