7. A Russian school reformer, Ivan Betskoy was rumored to be not only Catherine the Great’s close friend and ally but also her father, that is, until Catherine grew disinterested in Betskoy’s enlightenment ideas.

A. A Russian school reformer, Ivan Betskoy was rumored to be not only Catherine the Great’s close friend and ally but also her father, that is, until Catherine grew disinterested in Betskoy’s enlightenment ideas.
B. Ivan Betskoy, a Russian school reformer, not only was Catherine the Great’s close friend and ally – until, that is, Catherine grew disinterested in Betskoy’s enlightenment ideas – but was also rumored to be her father.
C. Rumored to be not only Catherine the Great’s close friend and ally but also her father, Ivan Betskoy, a Russian school reformer, until Catherine grew disinterested in Betskoy’s enlightenment ideas.
D. Not only Catherine the Great’s close friend and ally, Ivan Betskoy was rumored to be her father, that is, until she grew disinterested in Betskoy’s enlightenment ideas.
E. Ivan Betskoy was rumored to be not only Catherine the Great’s close friend and ally, that is, until she grew disinterested in Betskoy’s enlightenment ideas, but also her father.

A Russian school reformer, Ivan Betskoy was rumored to be not only Catherine the Great’s close friend and ally but also her father, that is, until Catherine grew disinterested in Betskoy’s enlightenment ideas.

Grammar issue presented: meaning is obscured; it is a run-on sentence, and subsidiary clause is wrongly structured.
The meaning of this complex sentence is confused in two respects: First, it suggests that Betskoy’s being Catherine’s friend/ally and his being her father were both rumors, when in fact it was only her paternity that was the subject of rumors. Secondly, until Catherine grew disinterested in Betskoy's enlightenment ideas refers only to the ending of their friendship; however, it follows two qualifiers: close friend and her father. The rumors that Betskoy was Catherine’s father didn’t suddenly disappear after she grew tired of his ideas. Though punctuation is not normally a focus of GMAT sentence correction questions, in this question one piece of punctuation needs attention: the clause that is, until Catherine grew disinterested in Betskoy’s enlightenment ideas can create a run-on sentence if preceded by a mere comma.That same clause is better begun with the conjunction until than by that is, because that is means “by way of explanation,” and the reader has no sense of there being anything to explain before until introduces a change in the relationship between Betskoy and Catherine.

1. A Russian school reformer, Ivan Betskoy was rumored to be not only Catherine the Great’s close friend and ally but also her father, that is, until Catherine grew disinterested in Betsoky’s enlightenment ideas.
   Meaning clear? NO: also her father, that is until Catherine grew disinterested... plus confusion as to what was rumored.
   
2. Ivan Betskoy, a Russian school reformer, not only was Catherine the Great’s close friend and ally – until, that is, Catherine grew disinterested in Betskoy’s enlightenment ideas – but was also rumored to be her father.
   Meaning clear? YES
   
3. Rumored to be not only Catherine the Great’s close friend and ally but also her father, Ivan Betskoy, a Russian school reformer, until Catherine grew disinterested in Betskoy’s enlightenment ideas.
   Meaning clear? NO: confusion over what was rumored and what changed after Catherine grew disinterested...
   Additional errors? Sentence fragment.
   
4. Not only Catherine the Great’s close friend and ally, Ivan Betskoy was rumored to be her father, that is, until she grew disinterested in Betskoy’s enlightenment ideas.
   Meaning clear? NO: to be her father, that is until Catherine grew disinterested... Also, removing a Russian school reformer makes it difficult to understand Betskoy's enlightenment ideas.
   Additional errors? Faulty parallelism: missing but also.
   
5. Ivan Betskoy was rumored to be not only Catherine the Great’s close friend and ally, that is, until she grew disinterested in Betskoy’s enlightenment ideas, but also her father.
   Meaning clear? NO: Still unclear whether the rumor relates only to Catherine's paternity, and also as to whether she and Betskoy were ever friends.
   Additional errors? Run-on sentence and bad clause construction:
   ...close friend and ally, that is until... - that is doesn't refer to friend and ally but to the clause introduced by until.

(B) is the only choice that properly conveys the meaning of the sentence.

Q.6 Hard

Q.8 Hard