A multiple choice

All of the flowers now raised here have developed from those___in the forest.
A.once they grew B.they grow once
C.they once grow D.once grow

ABCD, which one is the correct answer?

Are you sure none of the choices are correct?

But this is from an exer ise book.

"Once grown" has the sense of "once cultivated" -- that is, once grown by man in the forest.

If the flowers now raised here were developed from forest wildflowers, then "which once grew" is the correct way to express this.

None of the given answers makes a grammatical sentence, no matter whether they were cultivated in the forest or not.

McTag, I'm flattered!