Who is they?
Apple indicated that the Siri program would not be available for previous IPhones because they do not have the capabilities to run such a program.

A:
previous IPhones

Who is they?
The judges monitor the performances of the competitors to measure their abilities, so they need to be able to impress them with their skills.

A:
the competitors

Who is they?
Four wheel drive cars are used for rally racing instead of rear wheel cars because they are better for off-road racing.

A:

Four wheel drive cars