**Core Concept**
The National Health Mission (NHM) introduced the Accredited Social Health Activist (ASHA) worker program to strengthen the primary healthcare system in India. ASHA workers are community health workers who act as a bridge between the community and the public health system.

**Why the Correct Answer is Right**
ASHA workers undergo a three-day training program, followed by a refresher course after six months. This training focuses on essential skills such as maternal and child health, family planning, and prevention of infectious diseases. The training curriculum is designed to equip ASHA workers with the knowledge and skills necessary to perform their duties effectively.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as the training duration for ASHA workers is not more than 3 days.
**Option B:** This option is incorrect as it does not specify the correct duration of training for ASHA workers.
**Option C:** This option is incorrect as it mentions a longer duration of training than required for ASHA workers.

**Clinical Pearl / High-Yield Fact**
It is essential for ASHA workers to receive regular refresher courses to update their knowledge and skills, ensuring they continue to provide effective support to the community.

**Correct Answer: D. 3 days**