which of the following is the correct way to print the slug property

which of the following is the correct way to print the  slug property

Choose correct from the following
which of the following is the correct way to print the  slug property of $fisrtTag object in this code snippet?
$tags=wp_get_tags($post->ID);
$firstTag=$tags[0];

1. $fistTag->slug
2. $fistTag.slug
3. $fistTag[0][‘slug’]
4. $fistTag[‘slug’];

The right answer is :
$fistTag->slug