In an electric circuit, a rheostat is commonly used to change which of the following quantities?

1. A rheostat is a variable resistor with a sliding contact. 2. Moving the slider changes the length of wire in the circuit, changing the resistance. 3. By varying resistance, it controls the current; the quantity it directly changes is resistance. _Source: RRB Group D CEN-02/2018 PYQ, Q.2._