Why $BH^{-} _ {4}$ and $NH_4^{+}$ are isolobal.

Question

$\begin{array}{1 1} \text{(a) They are $sp^3$ hybridised and have tetrahedral (having 4 lobes) shapes.} \\ \text{(b) They are $sp^2$ hybridised and have trigonal shape.}\\ \text{(c) They are $sp$ hybridised and have tetrahedral (having 4 lobes) shapes.} \\\text{(d) They are $sp^3$ hybridised and have trigonal shape} \end{array}$