What best describes a pull-up or pull-down resistor?
A resistor in a keying circuit used to reduce key clicks
A resistor connected to the positive or negative supply used to establish a voltage when an input or output is an open circuit✓Correct answer
A resistor that ensures that an oscillator frequency does not drift
A resistor connected to an op-amp output that prevents signals from exceeding the power supply voltage
Explanation
A pull-up or pull-down resistor ties a line to the positive or negative supply through a resistance, so the line holds a defined logic level whenever nothing is actively driving it, while a real driver can still override it. The other choices describe a key-click filter, an oscillator-stability component, and output clamping, none of which is this resistor's function.