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

[EX Q]: Mountain zebras can live up to _ days without drinking water.
[EX A]: three

[EX Q]: Diatoms look like _ shells that fit together.
[EX A]: two

[EX Q]: Biological islands are of _ general types, geographical and ecological.
[EX A]:
two