An electric current can flow through material A but not material B

This statement suggests that material A is a conductor, while material B is an insulator.

1. Electric current is the flow of electric charge, usually carried by electrons.

2. In conductive materials, such as metals, the outermost electrons in their atoms are loosely bound, which allows them to move freely and carry electric charge. This is why electric current can flow through these materials.

3. On the other hand, in insulating materials, the electrons are tightly bound to their atoms. They cannot move freely, so they cannot carry electric charge. This is why electric current cannot flow through these materials.

4. Therefore, material A must be a conductor and material B must be an insulator.