The following sentence has been split into four segments. Identify the segment that
contains a grammatical error.
By the time I turn thirty / I would had visited every / continent in the world and have
gained / a wealth of knowledge and experience.

Correct option is C

The error in the sentence is in segment (c) "I would had visited every." The correct form should be "I would have visited every." The phrase "would had" is grammatically incorrect; it should be "would have" to form the correct conditional perfect tense.
· In conditional sentences, "would" is always followed by the base form "have" and then the past participle of the verb, in this case, "visited." Therefore, the corrected segment should be "I would have visited every."