#4: It's gotta be c, the ratchet pads. No other answer makes better sense.
#9: True. Thumb-cocking the hammer causes the toe of the hammer to rotate the trigger toward the rear of the trigger-guard.
#13: It's c, the locking bolt. It gets in the way of hammer movement.
#14: The more screws, the earlier the manufacture, so the answer is a.
#15: It's d, the hammer.
#16: It's a, upward.
Take a look at the interior parts of a typical, older, S&W revolver by clicking on: http://en.wikipedia.org/wiki/File:Fifthchangelock.jpg