If a,b,c,d are positive real number , then least value of $\;(a+b+c+d)\;(\frac{1}{a}+\frac{1}{b}+\frac{1}{c}+\frac{1}{d})\;$ is :

Question

$(a)\;4\qquad(b)\;8\qquad(c)\;16\qquad(d)\;2$