**Core Concept**
The question is testing the student's knowledge of dental instruments, specifically the types of needles used in endodontics for root canal procedures. A shortened spinal tap needle assembled with an H-file is a specialized instrument used for mechanical preparation of the root canal.

**Why the Correct Answer is Right**
The correct answer, option B, is a combination of a shortened spinal tap needle and an H-file. The spinal tap needle is modified to have a smaller diameter and length, allowing for easier navigation through the root canal. The H-file is a type of endodontic instrument used for mechanical preparation of the root canal, and when assembled with the shortened spinal tap needle, it enables simultaneous filing and irrigation of the canal. This allows for efficient and effective removal of pulp tissue and debris.

**Why Each Wrong Option is Incorrect**
**Option A:** A spinal tap needle is not typically used in endodontics, and it is not designed for mechanical preparation of the root canal.

**Option C:** A side vent needle is used for irrigation, but it is not assembled with an H-file, and it is not designed for mechanical preparation of the root canal.

**Option D:** A needle with a file for simultaneous filing and irrigation is not a standard instrument in endodontics, and it is not specifically designed for root canal procedures.

**Clinical Pearl / High-Yield Fact**
When assembling an H-file with a shortened spinal tap needle, it's essential to ensure that the file is securely attached to the needle to prevent breakage or damage to the instrument.

**✓ Correct Answer: B. Shortened Spinal tap needle assembled with H file**