Answer: az aks install-cli

The correct command to install the kubectl client on a machine with Azure CLI installed for managing an Azure Kubernetes Service (AKS) cluster is 'az aks install-cli'. Option A is the correct answer. This command downloads and installs the kubectl CLI, which is used to manage Kubernetes clusters. The other options are incorrect because they either refer to different commands or incorrect methods of installing kubectl.

Author: LeetQuiz Editorial Team