**Core Concept**
The development and eruption of teeth are closely related to the growth and development of an individual. The presence of 20 permanent teeth and 8 temporary teeth indicates a certain stage of dental development, which can be correlated with the child's age.

**Why the Correct Answer is Right**
Typically, children start losing their primary teeth (temporary teeth) at the age of 6 and continue to lose them until they are about 12 years old. By the age of 12, most children have lost all their primary teeth and have a full set of 28 permanent teeth, which are then followed by the eruption of 4 wisdom teeth. The presence of 20 permanent teeth and 8 temporary teeth suggests that the child is likely in the mixed dentition stage, which usually occurs between the ages of 6 to 12.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the presence of 20 permanent teeth and 8 temporary teeth does not indicate a child who has recently lost all their primary teeth (usually occurs after the age of 12).
**Option B:** This option is incorrect because the presence of 20 permanent teeth and 8 temporary teeth does not indicate a child who has not yet lost any primary teeth (usually occurs before the age of 6).
**Option C:** This option is incorrect because the presence of 20 permanent teeth and 8 temporary teeth does not indicate a child who has a full set of permanent teeth without any temporary teeth (usually occurs after the age of 12).

**Clinical Pearl / High-Yield Fact**
A child with 20 permanent teeth and 8 temporary teeth is likely in the mixed dentition stage, which is a normal part of dental development that usually occurs between the ages of 6 to 12.

**Correct Answer: C. 12 years old**