Find the part of the sentence that contains an error: It was the misalignment between projected and actual data (1)/ that cast doubt not only on the calculations (2)/ but also on the assumptions that (3)/ underlied the funding strategy. (4)

Correct — D. The error is the verb underlied. Underlie is irregular and follows lie (to recline): underlie, underlay, underlain.

The sentence is in the past (It was … that cast doubt), so part (4) should read that underlay the funding strategy.

There is no form underlied, so segment (4) carries the error → option (d).

Why the others are wrong

• (a)
  (1) — It was the misalignment between projected and actual data opens a correct cleft sentence, It was X that…, and between pairs its two items with and.
• (b)
  (2) — cast doubt is correct. Cast is the same in present and past, and with the singular subject misalignment it reads as past; the present would be casts.
• (c)
  (3) — but also on the assumptions matches not only on the calculations, with on + noun after both halves, so the pair is parallel. The relative that then introduces part (4).

Spot-the-error items reward checking each verb form against its principal parts. Verbs built on an irregular verb usually keep its pattern: undergo, underwent; overcome, overcame. Underlie follows lie, so its past is underlay.

Two look-alike verbs are easy to confuse. Underlie (to be the basis of) goes underlie, underlay, underlain. Underlay (to put something beneath) goes underlay, underlaid.

Key facts

• Underlie: underlie → underlay (past) → underlain (past participle).
• Lie (to recline): lie → lay → lain, the pattern underlie follows.
• Underlay (to place beneath): underlay → underlaid.
• Cast keeps one form for present, past and past participle.

Common traps

• Correcting underlied to underlaid. That is the past of underlay, a different verb meaning to place beneath.
• Flagging cast in part (2) as a missing -ed. Cast is the same in present, past and past participle.

No directly related past PYQ was found.