Directions: In the sentence below, identify the part containing a grammatical or idiomatic error, if any. Ignore punctuation errors.

The collection of antique coins were (A) / carefully stored in (B) / a locked cabinet (C) / at the museum. (D) / No error (E)

The correct option is A.

Explanation:
To determine the part containing the grammatical error, we need to examine the subject-verb agreement in the given sentence:

"The collection of antique coins were (A) / carefully stored in (B) / a locked cabinet (C) / at the museum. (D)"

1. Identify the Subject: The subject of the verb is the noun phrase "The collection of antique coins". The main head noun in this phrase is "collection", which is a singular collective noun.
2. Identify Prepositional Modifiers: The phrase "of antique coins" is a prepositional phrase modifying the singular head noun "collection". The plural noun "coins" acts as the object of the preposition "of", so it does not determine the verb form.
3. Check Subject-Verb Agreement: A singular subject requires a singular verb. Therefore, the singular noun "collection" must take the singular verb "was" rather than the plural verb "were".

Corrected Sentence:
"The collection of antique coins was carefully stored in a locked cabinet at the museum."

Hence, part (A) contains the grammatical error.