The long run average cost curve $is$ the same $as$ the long run marginal cost curve

$A.$ when the production function exhibits increasing returns $to$ scale

$B.$ when the production function exhibits decreasing returns $to$ scale

$C.$ when the production function exhibits constant returns $to$ scale

$D.at$ the point long run marginal costs are a minimum

$E.at$ the point $of$ tangency between the isoquant and iso$-cost$ curve