At room temperature the current in an intrinsic semiconductor is due to

The correct answer is D: Holes and electrons.
Here's why:
Intrinsic semiconductors are pure semiconductors, meaning they haven't been doped with any impurities.
At room temperature, some of the electrons in the semiconductor gain enough energy to break free from their bonds.
When an electron breaks free, it leaves behind a hole in the crystal structure.
Both the free electrons and the holes can move through the material under the influence of an electric field.
Therefore, the current in an intrinsic semiconductor at room temperature is due to the movement of both holes and electrons.
Ions are not the primary charge carriers in intrinsic semiconductors.