Which sentence is an example of a pun?

1).i want to look for my watch, but i can never seem to find the time.
2).by making cupcakes for them, i can kill two birds with one stone.
3).it is often wise to keep your friends close and your enemies closer.
4).she explained the novel so well that she hit the nail on the head.
5).she did not with dinner because too many cooks can spoil the broth.

if this is a true or false question its true

the following key ideas correctly express the key sentence.

restate key idea: most people can learn to swim in ten short lessons.

restate key idea: the majority of water-accident victims require mouth-to-mouth breathing.

restate key idea: an empty, tightly closed gallon jug will support a tired swimmer.  

restate key idea: first aid is to prevent accidents as well as assist in rescue.

explanation: the key idea needs to have the same topic as the key sentence (drowning and safety).