1. Identification of Error: Redundancy ('reason why', 'is because'), Subject-Verb Agreement (incorrect tense for 'is'), and Parallelism (non-parallel verb forms).
2. Grammatical Rule: "Reason why" and "reason is because" are tautological phrases; the correct constructions are typically "The reason... is that..." or "The reason... is due to...". The verb in the main clause must agree in tense with the overarching context. Parallel elements in a list or compound structure must be presented in the same grammatical form.
3. Option Elimination:
A. Incorrect — This option retains all the identified errors: redundancy ("reason why" and "is because"), subject-verb disagreement (using 'is' instead of 'was' to match the past tense context), and a parallelism error ('neglected' is not parallel with 'ignoring').
B. Incorrect — While this option corrects the parallelism error by changing 'ignoring' to 'ignored', it retains the fundamental redundancy of "reason why... was because," which is still grammatically flawed.
C. Correct — This option comprehensively addresses all errors. It removes the redundant 'why' and replaces 'is because' with 'was that', forming a grammatically sound and non-redundant structure ("the principal reason... was that"). It also corrects the subject-verb agreement by changing 'is' to 'was' to align with the past tense context. Finally, it establishes correct parallelism by ensuring both verbs are in the past tense ('neglected' and 'ignored').
D. Incorrect — This option correctly eliminates the redundancy by using "was due to" and establishes parallelism between the gerunds ('neglecting' and 'ignoring'). However, changing 'neglected' to 'neglecting' while the original sentence used 'neglected' (a past tense verb) is not the most direct or preferred method of correcting the original parallelism in CAT-style questions when 'was that' followed by two parallel past tense verbs is a clearer and more concise solution that also maintains the original verb tense of the first parallel element.