Which of the following fluoro-compounds is most likely to behave as a Lewis base?

A Lewis base is a species that can donate a pair of electrons.${\text{BF}}_3$: Boron has 6 electrons, so it is electron-deficient (Lewis acid).${\text{SiF}}_4$: $\text{Si}$ is in group 14, no lone pairs on $\text{Si}$.${\text{CF}}_4$: $\text{C}$ is in group 14, no lone pairs on $\text{C}$.${\text{PF}}_3$: Phosphorus (group 15) has 5 valence electrons. It uses 3 for bonding with $\text{F}$ and has one lone pair remaining. Thus, it can act as a Lewis base.