Directions: Each question below has two blanks, each blank indicating that something has been omitted. Choose the set of words, for each blank that best fits in the meaning of the sentence as a whole.

Auroras are natural light, displays in the sky usually ________ at night, ________ in the Polar regions.

The correct answer is C. Auroras are natural light displays that are 'observed' (watched/seen) at night, and they occur 'only' in polar regions (Arctic and Antarctic). This combination captures both the visual nature of auroras and their geographical restriction. Options like 'watch, upward' or 'found, most' don't capture the precise meaning - auroras aren't typically described with 'upward', and 'most' in polar regions would suggest they also occur elsewhere, which is incorrect.