**Core Concept**
A leading question is a type of question that is phrased in a way that suggests a specific answer or influences the respondent's response. In the context of forensic medicine, particularly in the investigation of crimes, leading questions can be used to elicit information from witnesses, suspects, or victims. However, they can also contaminate the evidence and compromise the integrity of the investigation.

**Why the Correct Answer is Right**
**Option C:** "Whether it is caused by knife" is a leading question because it implies a specific object (knife) as the cause of the injury. This type of question can lead the respondent to provide an answer that confirms the investigator's preconceived notion, rather than allowing them to provide a neutral or objective account of the events. In a forensic investigation, it is essential to ask open-ended, non-leading questions to gather accurate and unbiased information.

**Why Each Wrong Option is Incorrect**
**Option A:** "How did you get cuts on T shirt" is not a leading question because it is a neutral inquiry that seeks information about the circumstances surrounding the injury. It does not imply a specific cause or object.
**Option B:** "Cause of injury" is a factual question that seeks information about the underlying reason for the injury. While it may be a leading question in certain contexts, in this case, it is a straightforward inquiry that does not imply a specific cause or object.
**Option D:** "Size of incised wound" is a factual question that seeks information about the physical characteristics of the wound. It is not a leading question because it does not imply a specific cause or object.

**Clinical Pearl / High-Yield Fact**
In forensic medicine, it is essential to use open-ended, non-leading questions to gather accurate and unbiased information from witnesses, suspects, or victims. This can help prevent the contamination of evidence and ensure the integrity of the investigation.

**✓ Correct Answer: C. Whether it is caused by knife**