TASK DEFINITION: In this task, find the most appropriate number to replace the blank (indicated with _ ) and express it in words.
PROBLEM: Morocco has _ perennial rivers and many dams have been built with potential for power generation.

SOLUTION: four

PROBLEM: Glycolysis occurs in the cytoplasm and produces _ pyruvic acid.

SOLUTION: two

PROBLEM: Postal codes are six characters long and are a mixture of _ letters and three numbers.

SOLUTION:
three