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

[EX Q]: Conserved residues make similar contacts in _ repressor-operator complexes.
[EX A]: two

[EX Q]: Green energy comes in _ basic forms.
[EX A]: two

[EX Q]: Plants lose vigor and decline in abundance within _ to four years.
[EX A]:
three