$\begin{array}{1 1}(a)\;\text{Stronger }\sigma\text{ bond between B and F in }BF_3\text{ as compared to that between C and F in }CF_4\\(b)\;\text{Significant }p\pi-p\pi\text{ interaction between B and F in }BF_3\text{ whereas there is no possibility of such interaction between C and F in }CF_4\\(c)\;\text{Smaller size of B-atom as compared to that of C-atom}\\(d)\;\text{Lower degree of }p\pi-p\pi\text{ interaction between B and F in }BF_3\text{ than that between C and F in }CF_4\end{array}$