TASK DEFINITION: Given a sentence, fill out the missing word with a 'no' or a number (between zero and ten). You should write the numbers with english alphabet, like: four instead of 4.
PROBLEM: Erosion is divided into ____ main categories, water and wind.

SOLUTION: two

PROBLEM: Tobacco companies account for ____ of the five biggest billboard advertisers in the country.

SOLUTION: four

PROBLEM: Light can provide energy by ____ fundamentally different mechanisms.

SOLUTION:
two