The sentence below is partitioned into four segments. Determine which segment, if any, contains a grammatical error and select it. If the sentence is grammatically correct, select 'No error'.

Certain students do not enjoy theoretical proposed(A) / ideas because they do not (B) / wish to study theories that (C) / are unproven or have no practical use (D) .

The correct option is A.

Explanation:
Segment (A) contains a grammatical error: "Certain students do not enjoy theoretical proposed".

In the phrase "theoretical proposed ideas", the word "theoretical" (an adjective) is used directly before "proposed" (a participle functioning as an adjective). An adjective cannot modify another adjective/participle; an adverb is required to perform this function. Therefore, the adjective "theoretical" should be replaced with the adverb "theoretically" to correctly modify "proposed", making the correct phrasing "theoretically proposed ideas".