Counter-Offer: question from Mock Exam BPP exam tick

Dear Mike

Could you kindly help with below question?

Under the UN Model Law on Contracts for the International Sale of Goods, what is the effect of a counter-offer on the original offer?

A Acceptance of the original offer as it stands
B Acceptance of the original offer with new terms introduced
C Rejection of the original offer
D No effect on the original offer

My answer is C based on the art 19 (1) of UNCITRAL:

A reply to an offer which purports to be an acceptance but contains
additions, limitations or other modifications is a rejection of the offer and
constitutes a counter-offer.

The book answer is below for following explanation

B. Under the Model Law the counter offer has the effect of introducing new terms into the original offer and these new terms will form part of the acceptance as long as the offeror does not object.

Based on my understanding the answer provided by the book is referring to Art 19 (2)

Art 19 (2) However, a reply to an offer which purports to be an acceptance
but contains additional or different terms which do not materially alter the
terms of the offer constitutes an acceptance, unless the offeror, without undue
delay, objects orally to the discrepancy or dispatches a notice to that effect.
If he does not so object, the terms of the contract are the terms of the offer
with the modifications contained in the acceptance

Should the counter offer be considered as a rejection of the original offer or an acceptance which contains different terms?

Thanks a lot in advance for your help
Best Regards

Gabbi