In this error spotting question, identify the part of the sentence that contains an error: The stream gurgled contentedly as it slowed to rounding the bend.

Introduction / Context:
This question tests your understanding of correct non finite verb forms (infinitives and gerunds) after verbs like slow. The sentence uses slowed to rounding, which sounds awkward and is not a standard pattern in English. You must identify which part of the sentence contains this error and understand how to correct it.

Given Data / Assumptions:
- Full sentence: The stream gurgled contentedly as it slowed to rounding the bend. - Part (1): The stream gurgled. - Part (2): contentedly as it. - Part (3): slowed to rounding the bend. - Part (4): No Error.

Concept / Approach:
The verb slow is typically followed either by an infinitive (to plus base verb) indicating purpose or result, such as slowed to stop, or by a preposition plus gerund, such as slowed before rounding the bend. The combination slowed to rounding is incorrect because it mixes the infinitive marker to with a gerund form rounding improperly. The error therefore lies in part (3).

Step-by-Step Solution:
Step 1: Focus on the phrase slowed to rounding the bend in part (3). Step 2: Recognise that to is usually followed by a base verb to form an infinitive, as in to round, not by a gerund. Step 3: Consider correct alternatives: slowed to round the bend or slowed before rounding the bend. Step 4: See that slowed to rounding combines to with a gerund, which does not match standard patterns. Step 5: Confirm that parts (1) and (2) are grammatically correct: The stream gurgled contentedly as it is a natural start to the sentence. Step 6: Conclude that the error is entirely located in part (3).

Verification / Alternative check:
Rephrase the sentence correctly: The stream gurgled contentedly as it slowed before rounding the bend. This version uses before plus gerund rounding, which is a standard pattern. Alternatively, you could write as it slowed to round the bend, using an infinitive. Both are acceptable. Slowed to rounding, however, does not fit either pattern and sounds unnatural, confirming that part (3) is wrong.

Why Other Options Are Wrong:
Part (1) The stream gurgled is a correct past tense clause describing the stream's sound. Part (2) contentedly as it logically and grammatically continues the sentence. Part (4) No Error cannot be chosen because there is a clear verb form problem in part (3).

Common Pitfalls:
Some students may overlook this kind of subtle error because the overall meaning of the sentence is understandable. Others may think any use of to plus ing is acceptable, confusing it with structures like be used to doing. In this sentence, however, to is an infinitive marker, not a preposition, so it must be followed by the base form of the verb. Remember to distinguish between to as a preposition (followed by a noun or gerund) and to as part of the infinitive (followed by base verb).

Final Answer:
The error is in part (3); the phrase slowed to rounding the bend is incorrect.