What is the difference between the following line-height settings?

line-height: 20px;
line-height: 2;

1.  The value of 20px will set the line-height to 20px. The value of 2 will set the line-height to twice the size of the corresponding font-size value.
2.  The value of 20px will set the line-height to 20px. The value of 2 is not valid.
3.  The value of 20px will set the line-height to 20px. The value of 2 will default to a value of 2px.
4.  The value of 20px will set the line-height to 20px. The value of 2 will set the line-height to 20% of the corresponding font-size value.

Correct Answer:

•  The value of 20px will set the line-height to 20px. The value of 2 will set the line-height to twice the size of the corresponding font-size value.