In an accident there is great loss of blood and there is no time to analyse the blood group which blood can be safely transferred?

In an accident there is great loss of blood and there is no time to analyse blood group. Which blood group can be safely transferred?

In case of emergency (e.g., serious accident with great blood loss) which blood group could be safely transfused?

Blood group AB can take blood from which blood groups ?

Blood group A can donate blood to which blood group ?

A person with blood group B requires blood. The blood group which can be given is

Blood group A person can