In this task, find the most appropriate number to replace the blank (indicated with _ ) and express it in words.

[EX Q]: Lightning can travel _ miles or more horizontally from the storm, then strike the ground.
[EX A]: six

[EX Q]: Some people have _ or four careers during their lives.
[EX A]: three

[EX Q]: Natural thallium is a mixture of _ isotopes.
[EX A]:
two