Which one of the following contains all Lewis acids?

Lewis acids are species that can accept a pair of electrons. AlCl3, Co3+, and BF3 are all Lewis acids: AlCl3 has an electron-deficient aluminum atom (only 6 electrons in valence shell), Co3+ is a cation with empty d-orbitals that can accept electron pairs, and BF3 has an electron-deficient boron atom with only 6 valence electrons. In the other options, NH3 is a Lewis base (donates lone pair on nitrogen), OH− is a Lewis base (donates electron pair from oxygen), H2O is a Lewis base (donates lone pair from oxygen), and F− is a Lewis base (donates electron pair). Therefore, only option (a) contains exclusively Lewis acids.