What is the difference between ls and ls $-$a commands?

a$.$ ls $-$a lists all files including hidden files, whereas ls only lists visible files

b$.$ ls $-$a lists visible files only, whereas ls lists all files including hidden files

c$.$ ls and ls $-$a commands are the same and list all files including hidden files

d$.$ ls and ls $-$a commands are the same and list visible files only