Sentence Correction (SC) | Re: More than 300 rivers drain into Siberia's Lake Baikal, which holds 20

In A, is it correct for modifier "more than all the North American Great Lakes combined" to come in that construction? To my knowledge, if the noun-modifier is modifying a noun or a clause, in this case, 20% of world's fresh water lakes, the modifier must be of the form " ,a FIGURE more than all the NA great lakes combined". Please clarify me. I got a couple of answers wrong because of lack of understanding in this particular concept. Thank you in advance.