The quantifiers each and every are a kind of determiner.
They have similar but not identical meanings.
Each means “every one, regarded individually”.
Every means “every one, regarded as a whole”.
Sometimes, each and every have the same meaning:
- Fashion changes each year.
- Fashion changes every year.
But often they are not exactly the same, as explained above.
Hence, the correct answer is (b) every as it tells us how often something happens/