Final answer:
A possible reason for disqualification in a deadlift attempt is not waiting for the command to start the lift and allowing the bar to stop on the thighs before full body erectness and locked knees.
Step-by-step explanation:
A possible reason for the disqualification of a deadlift attempt in powerlifting is when the lifter does not wait for the command to start the lift. The lifter must wait for the referee's signal before initiating the lift. This is to ensure fairness and standardization in the competition.
Another possible reason for disqualification is when the lifter allows the bar to stop on their thighs before their body is fully erect and knees locked. In a deadlift, the lifter must maintain continuous motion until they reach an upright position with locked knees.
The third option mentioned, wearing Nike shoes, is not a reason for disqualification. The choice of shoes does not affect the legality of the lift.
Therefore, the correct answer is a and b.