E6C07

What best describes a pull-up or pull-down resistor?

1. AA resistor in a keying circuit used to reduce key clicks
2. BA resistor connected to the positive or negative supply used to establish a voltage when an input or output is an open circuit
3. CA resistor that ensures that an oscillator frequency does not drift
4. DA resistor connected to an op-amp output that prevents signals from exceeding the power supply voltage

Pick an answer to check it.