Which C$++$ statement determines the length of the name string defined below and assign the value to the number variable?

int number $=0$;

string name $=$Hello$$;

a$.$

number $=$ name.len$()$;

b$.$

number $=$ name.size$()$;

c$.$

number $=$ size$($name$)$;

d$.$

number $==$ name.size$()$;