The given sentence has been split into different segments. Identify the segment that contains a grammatical error.

Had the architect planned (A)/ more carefully, the building (B)/ will have survived (C)/ the major earthquake. (D)/ No error

The correct option is C.

Explanation:
The given sentence follows the structure of an inverted third conditional, which is used to talk about unreal or hypothetical situations in the past.

The correct grammatical structure for an inverted third conditional sentence is:
Had + Subject + Past Participle (V3)... , Subject + would/could/might + have + Past Participle (V3)...

In the provided sentence:
• Segment (A) and (B): "Had the architect planned more carefully" is correct as the conditional clause.
• Segment (C): "will have survived" incorrectly uses the modal verb "will" instead of "would".
• Segment (D): "the major earthquake." completes the object of the sentence.

To make the sentence grammatically correct, "will have survived" must be replaced with "would have survived".

Hence, segment (C) contains the error.