Plot hole: When the survivors arrive in Las Vegas, all that is visible is the Strip. No other buildings are seen, even though Las Vegas has other high-rise buildings that are not on the Strip, and the level of sand that has built up is not substantial enough to have buried the entire city. (00:55:00)
Plot hole: In the scene where Alice breaks into the Umbrella compound she drives the vehicle through the truck wreckage and into the fence, knocking the fence down. However, she then has time to ferry everyone from the vehicle into the chopper, stand back and watch them fly away, then walk cautiously into the shanty shack and wait for the elevator to arrive. Meanwhile not a single zombie has chased her into the now breached compound. The zombies might be dumb, but if they see food they head straight to it until an obstacle stops them and the explosion would have only killed the ones in the immediate area. The ones behind the dead zombies would have charged at them as soon as the fire died down. (01:11:00)
Chosen answer: The reason that the cloned alices were put through the tests was their attempt to get a "perfect" clone of her. They knew that Alice was the key to taking back the zombie infestation, so they were trying to get the "perfect" clone. The perfect clone would have all of her memories and reactions, so they put the clones through that testing facility. If she made it out alive, then she was the perfect clone. If she didn't, then it was back to the drawing board.
Nick Bylsma