Which of these actions can be classified under incomplete lift?

Not locking out the bar during a lift is classified as an incomplete lift because it fails to meet a fundamental requirement of proper lifting technique. In powerlifting, each lift—whether it's the squat, bench press, or deadlift—has specific criteria that must be fully executed for the lift to be deemed successful. Locking out the bar means that the lifter has reached full extension of the joints involved (such as the elbows in the bench press or knees and hips in the deadlift) and has maintained control of the bar in a stable position. If this lockout isn't achieved, the lift does not demonstrate full muscle engagement and control, rendering it incomplete according to the standards set forth by governing bodies like the British Columbia Powerlifting Association.

The other actions, such as dropping the bar, touching the belt with the bar, and elbows bending during the lift, each involve different forms of errors or infractions that might incur a fail in judging, but they do not specifically indicate the lack of completion in a lift in the same clear manner that not locking out does.