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: Buses are ____ times as fuel efficient as cars.

SOLUTION: five

PROBLEM: Sexual maturity is between ____ and six years of age.

SOLUTION: three

PROBLEM: Arthropods are made up of ____ groups of living animals and one group of extinct animals.

SOLUTION:
four