it would be the -os form so it would say: Le doy las flores a ella.
So in English it would say I give them flowers.
A.) a mi cause it would say: I give flowers to me. and that doesn't make sense.
B.) a ella is correct because it makes sense. I give her the flowers.
C.) a ellos is incorrect because it doesn't make sense. I give them flowers.D.) a nosotros is incorrect because it does not make sence I give flowers to us.
~Good Luck~