**Core Concept**
In infants less than 2 months old, the normal respiratory rate is higher than in older children and adults, and fast breathing is a critical indicator of respiratory distress or infection.

**Why the Correct Answer is Right**
The World Health Organization (WHO) recommends that for infants less than 2 months old, fast breathing is defined as a respiratory rate of 60 breaths per minute or more. This is because infants have a higher metabolic rate and respiratory demand due to their rapid growth and development. Fast breathing in this age group may be an early sign of respiratory infections such as pneumonia or bronchiolitis, which require prompt medical attention.

**Why Each Wrong Option is Incorrect**
**Option A:** This is likely too low and would not be considered fast breathing in an infant less than 2 months old.
**Option B:** This is not the correct answer, as fast breathing is defined by a respiratory rate of 60 breaths per minute or more in this age group.
**Option D:** This is not the correct answer, as fast breathing is defined by a respiratory rate of 60 breaths per minute or more in this age group.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the definition of fast breathing in infants less than 2 months old is different from that in older children and adults, and healthcare providers should use the WHO guidelines to assess respiratory distress in this age group.

**Correct Answer:** D. 60 breaths per minute or more.