The following sentence has been split into four segments. Identify the segment that contains a grammatical error. My house / is more / spacious than / my sister.

The correct answer is my sister.

Step-by-step Explanation:
1. Analyze the Comparison: The sentence reads: "My house is more spacious than my sister." In this sentence, the property "My house" is being compared directly to the person "my sister".
2. Identify the Logical/Grammatical Error: This is a classic grammatical error known as a faulty comparison (or illogical comparison). You must compare similar things. A house (a physical structure) cannot be compared to a person (my sister) in terms of physical space or area.
3. How to Correct the Sentence: To make the comparison logical, the house of the speaker must be compared to the house of the sister. This can be corrected in one of the following ways:
- "My house is more spacious than my sister's." (where "sister's" implicitly refers to "sister's house")
- "My house is more spacious than that of my sister."
4. Conclusion: Since the segment "my sister" is what creates this faulty comparison, it is the part that contains the grammatical error.