"A 'pull up$\text{'}$ resistor is used in digital circuits to do what?"

The options provided are:

a$.$ To make sure the digital line is always high

b$.$ To keep the voltage at $0$ Volts

c$.$ To keep the signal "tied" high until the line is active $($goes low$)$

d$.$ To keep the voltage at $1$ Volt

e$.$ To keep the signal line "tied" low until the line is active $($goes hig