Which of the following fits gap (iii)?

Directions: Complete the passage by selecting the most suitable word/phrase from each list to fit the corresponding gap.

Black holes are the (i)______ objects in the Universe. A black hole (ii)_______ have a surface, like a planet or star. Instead, it is a region of space (iii)____ matter has fallen down on itself. This great fall results in a large amount of material packing up (iv)___ a really small area. The pulling force of this region is so great that nothing can escape – not even light.