$\left(\frac{a}{x}-b x\right)^{12}$ এর বিস্তৃতিতে মধ্যপদ কত ?

${ }^{12} C_{6} a^{6} b^{5}$

${ }^{12} C_{6} a^{6} b^{6}$

${ }^{11} C_{6} a^{6} b^{6}$

${ }^{6} \mathrm{C}_{5} \mathrm{a}^{6} \mathrm{~b}^{6}$