Structure shown below is $2$ D boron nitride $(BN)$ crystal, where the red atoms are $B$ and the blue atoms are N $.$ The two basis vectors are shown by the dashed lines, which have the same length and $60$ angle.

$(1)$ If $B-N$ bond length is $a.$ What is the length of the basis vector?

$(2)$ How many B and $N$ are there in the unit cell constructed by the basis vectors? What are their coordinates $($in the units of basis vectors$)?$

$(3)$ What is the area of the unit cell?

$(4)$ Draw the lattice and the conventional cell

$(5)$ What are the lattice parameters?