The correct answer is option 3, "I and II are correct".

Statement I is correct as asteroids are indeed rocky debris of varying sizes that orbit the Sun. They are remnants from the early solar system and can range in size.

Statement II is also correct. While most of the asteroids are small, some of them can indeed be large with diameters up to 1000 km.

Statement III, however, is incorrect. The main region where asteroids are found is not between the orbits of Jupiter and Saturn, but mostly situated in an area of space called the asteroid belt, which lies between the orbits of Mars and Jupiter. Thus, this option does not reflect the correct placement of main group of asteroids in the Solar System. The combination of statement I and II will make the option 3 the correct answer.