If the electric field at a point on the line between two charges is zero, what can you say about the charges?

the charges have opposite signs the charges have same magnitudes the charges have same signs the charges have different magnitudes

the charges have same signs

They must have the same sign of charge. This is because electric field is a vector quantity. For example, if both are positive, then the electric field points away from each charge and the resultant will be zero where they meet at the point between them.