The correct answer is
They are held together by strong attractions.
In a solid, in fact, the atoms/molecules are held together by atomic/molecular bonds, which are very strong, so that the atoms cannot move apart, but they can only vibrate around their position.
Instead, in liquids, atoms and molecules can slide past each other, but they are still close because there are still weak intermolecular forces acting between them. On the contrary, in gas, atoms are located very far apart and are free to move.
