In the following English sentence, identify the part that contains an error, or choose No error if the sentence is correct: His parents usually spent their summer in Ooty, but this year they are spending it in Darjeeling.

Introduction / Context:
This question checks your understanding of tense consistency and the use of present versus past forms to describe habitual actions. In English, general habits or routines are usually expressed in the simple present tense, while specific completed actions in the past use the simple past.

Given Data / Assumptions:
- Sentence: His parents usually spent their summer in Ooty, but this year they are spending it in Darjeeling. - Part A: His parents usually spent. - Part B: their summer in Ooty. - Part C: but this year they are spending it in Darjeeling. - Part D: No error.

Concept / Approach:
The adverb usually describes a regular habit over many years. In standard English, we use the simple present for such habits, for example, His parents usually spend their summer in Ooty. The second clause but this year they are spending it in Darjeeling describes an ongoing or special action this year, and uses the present continuous, which is correct. The error therefore lies in the mismatch between usually and spent in the first clause.

Step-by-Step Solution:
Step 1: Identify the time markers. Usually indicates a general habit, and this year indicates the current specific case. Step 2: For general habits, English uses the simple present: spend, not spent. Step 3: Examine Part A, His parents usually spent. This wrongly combines usually with a simple past verb. Step 4: The correct form should be His parents usually spend. Step 5: Part C, but this year they are spending it in Darjeeling, correctly uses present continuous for a special action this year. Step 6: Therefore, the error is in Part A.

Verification / Alternative check:
Rewrite the sentence with corrected tense: His parents usually spend their summer in Ooty, but this year they are spending it in Darjeeling. Now the first clause states a general habit, and the second clause describes an exception in the present. Both parts fit naturally with the time expressions usually and this year, confirming that the correction is valid.

Why Other Options Are Wrong:
Part B their summer in Ooty is a correct and natural phrase indicating place of vacation. Part C but this year they are spending it in Darjeeling correctly uses present continuous to describe what is happening this year. Part D No error is wrong because we have already identified an error in the verb tense in Part A.

Common Pitfalls:
A common mistake is to match the tense of both clauses mechanically, for example using spent in both, without noticing the role of usually and this year. Another pitfall is to think that usually can be freely used with past forms. While this is possible if you speak about past habits that no longer continue, here the second clause clearly refers to this year, so the habit is still current, and the simple present spend is required.

Final Answer:
The error is in Part A, which should read His parents usually spend.