@classmethod
def start(cls, resources, background=False):
    """Start a virtual machine."""
    if not isinstance(resources, (list, tuple)):
        resources = [resources]
    opers = []
    for item in resources:
        oper = cls.call('hosting.vm.start', cls.usable_id(item))
        if isinstance(oper, list):
            opers.extend(oper)
        else:
            opers.append(oper)
    if background:
        return opers
    instance_info = "'%s'" % ', '.join(resources)
    cls.echo('Starting your Virtual Machine(s) %s.' % instance_info)
    cls.display_progress(opers)
