Grafting is the process used to create many citrus, avocado, and pear trees,
ensuring a plant that is genetically identical to the original instead of producing a random hybrid of two trees, like natural pollination.
A) ensuring a plant that is genetically identical to the original
instead of producing a random hybrid of two trees, like natural pollination
"Instead of" means substitution/replacement, which is not the meaning of this sentence.
B) and ensures a plant that is genetically identical to the original but does not produce a random hybrid of two trees, as
is done in natural pollination
As what "is done"....the genetically identical plant or the hybrid?
C) ensuring a plant that is genetically identical to the original and
not producing a random hybrid of two trees, as in natural pollination
"Not producing" could be better worded. "As" should contain a working verb/clause.
D) ensuring a plant that is genetically identical to the original rather than producing a random hybrid of two trees, as natural pollination would
Correct. "As" can take on working verbs. "Rather than" can take on verbs and noun phrases; "instead of" cannot.E) and ensures a plant that is genetically identical to the original,
unlike natural pollination that produces a random hybrid of two trees
"Like" and "unlike" cannot take on clauses.