You have 50 virtual machines (VMs) running across 5 ESX Servers in a DRS Cluster in a Production environment for a number of weeks. Several VMs running on one of the ESX Servers suddenly blue-screen. Which of the following is the most likely cause of the failure?

Answer: A hardware problem on the ESX Server hosting the failed virtual machines

Explanation:
A vmkernel panic would cause all running virtual machines to go offline, whereas a hardware failure could cause the blue-screen event indicated.