Standardized tests in elementary school were once administered every

A) Standardized tests in elementary school were once administered every other year, but it was found by an educational commission to be both economical plus reliable to reduce the testing schedule to only two of the six elementary years.
Really a tough call i eleminated this on the sole basis that it modifies the other year due to which themeaning was wrong therefore out

B) Although standardized tests in elementary school were once administered every other year, an independent educational commission found that reducing the testing schedule to only two of the six elementary school years was both economical and reliable.
The meaning is perfect i couldn't find any obvios faults therefore let us hang on to it

C) Since standardized tests in elementary school were once administered every other year, reducing the testing schedule to only two of the six elementary years was found by an educational commission both economical and reliable to reduce the testing schedule to only those two years.
This is wordy akward and doesn't convey the right meaning

D) Once administered every other year in elementary school, an independent educational commission found that reducing the standardized testing schedule to only two of the six elementary school years was both economical and reliable.
This gives us a meaning as though independent educational commission is administrated twice a year Hence out

E) An independent educational commission, having found it to be both economical plus reliable to reduce the standardized testing schedule to only two of the six elementary school years, which were once administered every other year in elementary school.
The which addition is the problem here since it gives the meaning as though school years are administrated twicw a year which is not the case therefore out

Therefore IMO B