I am unable to understand meaning of below sentense .
Does this sentence indicates both the events i.e. effect of poison and writhing were simultaneously happening
a) For six hours, 20-year-old Sushma writhed in agony on the floor as the poison did its work.
Hense my Versoin is
b) For six hours, 20-year-old Sushma was writhing in agony on the floor as the poison had done its work.
This is because it was effect of poison which made her writhed on floor. So first action would be effect of poison and later writhing.