## Core Concept
Clostridium tetani is a type of bacteria that causes tetanus, a serious bacterial infection. The bacteria are characterized by their Gram staining properties, microscopic appearance, and growth requirements. Understanding these characteristics is essential for diagnosing and managing tetanus.

## Why the Correct Answer is Right
The correct statements about Clostridium tetani are that it is **Gram-positive (a)** and has a **drumstick appearance (b)** due to its distinctive morphology, which includes a terminal spore that gives it a characteristic shape. This appearance is a key feature for its identification.

## Why Each Wrong Option is Incorrect
* **Option C:** It grows in an **anaerobic environment**, not aerobic. Clostridium tetani is an obligate anaerobe, meaning it requires an environment without oxygen to grow.
* **Option D:** It is **Gram-positive (a)**, not Gram-negative. This makes option D incorrect.

## Clinical Pearl / High-Yield Fact
A critical point to remember is that Clostridium tetani spores are commonly found in soil and the gastrointestinal tracts of animals. Tetanus infection typically occurs through wounds contaminated with these spores, highlighting the importance of proper wound care and tetanus toxoid vaccination in preventing the disease.

## Correct Answer: B. a, b.