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

[EX Q]: New species are believed to arrive in the Mediterranean at the rate of _ to five annually.
[EX A]: four

[EX Q]: Beavers have an average of _ young once a year.
[EX A]: four

[EX Q]: Phosphates are made of one phosphorus atom surrounded by _ oxygen atoms.
[EX A]:
four