Spot the grammatical error in the sentence. Select the part (A–D) that contains an error; if the sentence is correct, choose ‘‘No error.’’ Sentence: An anti-extortion cell is opened by the district police headquarter six months ago as a precautionary measure.

Introduction / Context:
This error-spotting item checks proper tense selection for past-time references and awareness of collocations in formal administrative English. The phrase ‘‘six months ago’’ fixes the time in the past and therefore requires a past tense in the main clause.

Given Data / Assumptions:

• The event (opening a cell) happened ‘‘six months ago’’ (completed past time).
• Current sentence uses simple present passive ‘‘is opened’’ in part A.
• Other phrases are typical of government reports.

Concept / Approach:
When a finished action is anchored by a past-time adverbial like ‘‘ago,’’ we use simple past. In passive voice, the form is ‘‘was/were + past participle.’’ Using present passive with ‘‘ago’’ is ungrammatical. Also, ‘‘police headquarters’’ is a noun that often remains invariant in number; however, the key tested error is tense in A.

Step-by-Step Solution:
Identify the time marker: ‘‘six months ago’’ = past, completed.Match tense: present passive ‘‘is opened’’ → incorrect with ‘‘ago’’.Correct form: ‘‘was opened’’ (simple past passive).Acceptable recast: ‘‘An anti-extortion cell was opened by the district police headquarters six months ago as a precautionary measure.’’

Verification / Alternative check:
Try replacing ‘‘ago’’ with ‘‘today’’ or ‘‘now’’; only then would ‘‘is opened’’ make sense. With ‘‘ago,’’ native usage strongly favors ‘‘was opened.’’

Why Other Options Are Wrong:

• B: ‘‘district police headquarter’’ is slightly awkward (‘‘headquarters’’ preferred), but the primary tested error is tense in A.
• C: The time phrase is correct and consistent.
• D: Idiomatic and acceptable.

Common Pitfalls:
Ignoring adverbials like ‘‘ago’’ and choosing present forms in passive constructions; over-focusing on nouns and missing the core tense error.

Final Answer:
An anti-extortion cell is opened