Right option is (a) .navbar-toggle
The best I can explain: .navbar-toggle styles button that should open navbar on small screens, often used together with three .icon-bar classes to indicate a toggleable menu icon, .navbar-text vertical align any elements inside navbar that are not links. Left, top and right borders from the nav bar can be removed by .navbar-static-top. Alignment of nav links, text and buttons in the nav bar to the right can be done by .navbar-right.