How Will the Following CSS Rule Alter the Web Page

How will the following CSS rule alter the web page if it is applied in a style sheet
H1 { font-family: Arial, sans-serif }

A) All text in h1 elements will have the Arial font, while text in other elements will use a sans-serif font.
B) All text in h1 elements will have use a sans-serif font, while text in other elements will use Arial.
C) All text in h1 elements will have the Arial font if sans-serif is not supported by the system.
D) All text in h1 elements will use a sans-serif font if Arial is not supported by the system.