RISPOSTE I AM LEGEND
How did Anna get into Manhattan when the island had been quarantined?
There are any number of ways that she could have gotten to Manhattan. An unblocked tunnel, a swing or draw bridge that was merely retracted and not destroyed, by boat. There would have been no quarantine in effect when she entered as humanity had been destroyed at that point
The original ending of the film (which was changed) showed the survivors leaving New York City on the George Washington Bridge. If that bridge is still intact it would explain not only how Anna got onto the island, but how she got her car onto it as well.
If civilization had collapsed three years before how is there still electricity and running water?
A panoramic shot of the interior of Neville's dwelling shows several gas-fueled generators. He presumably uses these for electric power.
For water, he may have a system of purifiers, but that wouldn't explain the presence of water pressure. It is possible that even after three years, the water that had been present in the city's pipelines would still be there. After all, Neville is the only one using a water supply that was meant to serve hundreds of thousands of citizens.
Also, New York City's water comes from the Catskill Mountains. The water only needs to be pressurized if it's going above the height of the Catskills. As long as he stays out of skyscrapers, Neville will have no trouble pumping water; he will always be below the mountain.
