Question $4$

Which is the following creates a structure with fields of mass and density?

$S=$ struct$($mass$,[],$ density, $[])$;

$S=$ struct$(\text{'}$mass$\text{'},$ mass, 'density', density$)$;

S $=$ struct$(\text{'}$mass$\text{'},[],$ 'density', $[])$;

$S=$struct${(}^{\text{'}}mas{s}^{\text{'}},{?}^{\text{'}}densit{y}^{\text{'}})$;