TASK DEFINITION: In this task, find the most appropriate number to replace the blank (indicated with _ ) and express it in words.
PROBLEM: White sturgeon inhabit _ large river systems, all on the western coast of North America.

SOLUTION: three

PROBLEM: Jurassic rocks have _ outcrops in the area but they are identified by bore holes.

SOLUTION: no

PROBLEM: Most jet airplanes have two, _ or four engines, depending on aircraft size.

SOLUTION:
three