In the sentence below, four words are marked as (A), (B), (C), and (D). These words may not be placed in their correct positions. Select the option that gives the correct interchange of words needed to make the sentence grammatically and contextually meaningful.

Regular breakdown (A) and proper care are crucial (B) for preventing machinery maintenance (C) and ensuring peak operational efficiency (D).

The correct option is A-C.

Let's analyze the given sentence and the contextual placement of the highlighted words:

Original sentence: "Regular breakdown (A) and proper care are crucial (B) for preventing machinery maintenance (C) and ensuring peak operational efficiency (D)."

1. The phrase "regular breakdown" is contextually incorrect because a breakdown is an unwanted failure of machinery, not a routine action paired with "proper care".
2. The phrase "preventing machinery maintenance" is also illogical, as maintenance is a positive practice designed to keep equipment running smoothly, not something to prevent.
3. Swapping word (A) breakdown with word (C) maintenance restores the logical meaning of the sentence:
"Regular maintenance (A) and proper care are crucial (B) for preventing machinery breakdown (C) and ensuring peak operational efficiency (D)."

Therefore, interchanging A-C renders the sentence both grammatically correct and contextually meaningful.