Fill in the blank with an appropriate option.

One of his rules was to always ________and await instruction to enter.

knock

The correct option to fill in the blank is knock.

The sentence is about a rule that a person follows, which is to always knock on a door and wait for permission to enter. The word "knock" means to strike a door or other surface with the knuckles of a closed fist, typically to attract attention or gain entry.

The other options are not as appropriate:

• Rub means to move one's hand over a surface with a repeated back-and-forth motion. It would not be accurate to use "rub" in this context, as the person is not rubbing the door.
• Blink means to close and open the eyelids quickly. It would not be accurate to use "blink" in this context, as the person is not blinking at the door.
• Resist means to oppose or try to prevent something. It would not be accurate to use "resist" in this context, as the person is not resisting the door.