In the following question, one part of the sentence may contain a grammatical error. Read the sentence carefully and identify the part that has an error, if any. My sister has been / interested in medicine / ever since she was a child / No error

Introduction:
Error spotting questions do not always contain an error; sometimes the correct choice is "No error". This particular sentence describes a continuing interest that began in childhood and continues up to the present. The question tests your understanding of present perfect tense combined with time expressions like "ever since".

Given Data / Assumptions:
- The sentence is split as: "My sister has been", "interested in medicine", "ever since she was a child", and "No error".
- Combined, the sentence reads: "My sister has been interested in medicine ever since she was a child."
- We assume standard grammar rules about present perfect tense and time clauses beginning with "since".

Concept / Approach:
When an action or state began in the past and continues up to the present, English commonly uses the present perfect tense. The structure "has been interested" expresses a state of interest that started earlier and still exists. The phrase "ever since she was a child" correctly marks the starting point in the past. The approach is to check each segment for tense correctness, prepositions, and word order, and then decide whether any correction is needed.

Step-by-Step Solution:
Step 1: Look at part A, "My sister has been". This introduces the subject and uses the auxiliary verb "has been" needed for present perfect passive or stative constructions.Step 2: Check part B, "interested in medicine". This is the correct participle and preposition combination: "interested in" plus the field of interest.Step 3: Examine part C, "ever since she was a child". The phrase "ever since" followed by a past tense clause is acceptable and natural.Step 4: Put the sentence together: "My sister has been interested in medicine ever since she was a child." It sounds natural and grammatically correct.Step 5: Conclude that there is no mistake in any of the parts, so the correct choice is "No error".

Verification / Alternative check:
You can verify the tense choice by thinking of similar sentences, such as "I have been interested in music since I was ten," which is clearly correct. If you change the tense incorrectly, for example "My sister is interested in medicine ever since she was a child," the sentence sounds wrong because present simple does not fit with "ever since". Also, using past tense alone, "My sister was interested in medicine ever since she was a child," would wrongly suggest that the interest has ended.

Why Other Options Are Wrong:
Option A is correct because "has been" is the right auxiliary structure. Option B is correct because "interested in medicine" uses the standard preposition "in" with "interested". Option C is correct because "ever since she was a child" correctly uses past tense for the point in time when the interest began. Therefore, none of the first three parts contain an error, and the only correct choice is option D, "No error".

Common Pitfalls:
Many students feel uncomfortable when the correct answer is "No error" and therefore try to force an error where there is none. Others may incorrectly think that "has been interested" should be "is interested", without considering the time expression "ever since", which requires a perfect tense to show continuity. To avoid such mistakes, always test alternative forms and check which one best expresses an action or state that started in the past and continues into the present.

Final Answer:
The sentence is already correct in all its parts, so the right choice is No error.