**Core Concept**
The question is testing the knowledge of hemoglobin F (HbF) levels in infants. HbF is a fetal hemoglobin that is produced during fetal development and is primarily responsible for transporting oxygen from the mother's bloodstream to the fetus. After birth, the production of HbF gradually decreases, and adult hemoglobin (HbA) takes over as the primary oxygen-transporting protein.

**Why the Correct Answer is Right**
In a 6-month-old infant, the level of HbF is expected to be relatively low because the infant's bone marrow starts producing adult hemoglobin (HbA) at a faster rate. The correct level of HbF in a 6-month-old infant is around 1-3%. This is because the infant's bone marrow starts to switch from producing fetal hemoglobin to adult hemoglobin during the first few months of life.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the level of HbF in infants typically decreases after birth, and a level of 70-80% is not consistent with normal development.
* **Option B:** This option is incorrect because the level of HbF in infants typically decreases after birth, and a level of 50% is not consistent with normal development.
* **Option C:** This option is incorrect because the level of HbF in infants typically decreases after birth, and a level of 0-1% is not consistent with this age group.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the level of HbF in infants decreases gradually after birth, and a normal level at 6 months is around 1-3%. This knowledge is crucial for diagnosing and managing conditions such as beta-thalassemia major, where elevated HbF levels can be a diagnostic clue.

**Correct Answer:** C. 1-3%