The correct answer is B. Permanent and available at all times.
Standing army is termed as army which is professional and permanent. It is being composed of soldiers who are full-time.
During the time of peace this army is not disbanded. Standing army is different from army reserves in that, they are enrolled for long term and they are active during a time when there is natural disaster or in time of wars.
They are temporary which means they can be disbanded when war is over. Ancient Greece were the first standing armies which were known in Europe.