Using Big$-$O notation, indicate the Order of the following for the worst case. State any assumptions you make.

After arriving at a party with n people present, you shake hands with everyone there.

Everyone in a room with n people shakes hands with everyone else in the room.

You climb a flight of n stairs.

You slide down the banister next to a staircase with n stairs.

After entering an elevator in a building with n floors, you press a button to choose a floor.