Error spotting in an English grammar sentence: The writer of this poetry is Wordsworth. Identify which part of the sentence is grammatically incorrect or decide that there is no error.

Introduction / Context:
This question checks the learner's knowledge of countable and uncountable nouns as well as appropriate collocations in English. The sentence talks about a famous English poet, Wordsworth, and asks you to decide if the expression used for his work is grammatically and stylistically correct in standard English. Error spotting items like this are common in competitive exams to test subtle points of noun usage.

Given Data / Assumptions:
- Sentence: The writer of this poetry is Wordsworth.
- Part (a): The writer
- Part (b): of this poetry
- Part (c): is Wordsworth
- Part (d): No error
We assume that the question aims at standard British or international English rather than highly informal speech.

Concept / Approach:
The noun poetry is generally uncountable and refers to the literary art in general. When we refer to a specific piece, we normally say poem, not poetry. Therefore, the phrase writer of this poetry sounds unnatural and incorrect in formal English. The natural expressions are writer of this poem, author of this poem, or writer of this piece of poetry. Parts (a) and (c) are structurally sound. The focus must therefore be on the noun phrase in part (b).

Step-by-Step Solution:
Step 1: Check part (a) The writer. This is a simple noun phrase and is correct. Step 2: Check part (b) of this poetry. Here, this is a demonstrative determiner that normally points to a single countable item. Step 3: Recall that poetry is usually uncountable and refers to the art form as a whole. To refer to one item we say poem. Step 4: Therefore, the correct expression should be of this poem or of this piece of poetry. Step 5: Check part (c) is Wordsworth. This link between subject and complement with the verb be is grammatically correct. Step 6: Since only the noun choice in part (b) is unacceptable, the error lies in part (b) only.

Verification / Alternative check:
A corrected sentence can be written as: The writer of this poem is Wordsworth. This is idiomatic English and clearly states that Wordsworth composed the particular poem in question. Another possible correction is: The writer of this piece of poetry is Wordsworth, which still treats poetry as uncountable but inserts an extra quantifying phrase piece of. Both alternatives confirm that the original phrase of this poetry is faulty and needs correction.

Why Other Options Are Wrong:
- Error in part (a) only: The writer is a correct and natural phrase; there is no error here.
- Error in part (c) only: Is Wordsworth is a grammatically perfect predicate and uses the correct proper noun, so it is correct.
- No error in the sentence: This would be correct only if of this poetry were acceptable, but in formal exam English it is not.
- Error in more than one part: Only part (b) needs to change, so claiming multiple errors is wrong.

Common Pitfalls:
Learners sometimes confuse poem and poetry, treating both as interchangeable. They may also ignore subtle collocation issues if the overall meaning is clear. However, competitive exams reward precision. Whenever a demonstrative like this or that is directly followed by a normally uncountable noun, it is worth checking whether a countable form such as piece, bit, or a different noun like poem should be used instead.

Final Answer:
Correct option: Error in part (b) only.