Sentence Correction (SC) | Ernst Haeckel held the individual development of biological organisms,

Magoosh Official Explanation:

A question about Ernst Haeckel, the biologist responsible for the idea "Ontogeny recapitulates phylogeny."

Split #1a: "held" +[infinitive] vs. "held" + "that"-clause. Choices (A) & (B) have the former, and the remaining three choices have the latter. The construction "hold P to be Q" is highly suspect: while it may appear in some contexts, it would never be part of a correct answer on the GMAT. What we have in
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