$\;A_{1},A_{2}\;,....\;A_{n}\;$ are fixed +ve real number such that $\;A_{1}\;.A_{2}\;..\;A_{n}=k$ , then $\;A_{1}+2A_{2}+\;...\;nA_{n}$ can not be than :

Question

$(a)\;n!\;k\qquad(b)\;n\;(n!k)^{\frac{1}{n}}\qquad(c)\;k^{\frac{1}{n}}\qquad(d)\;None\;of\;the\;above$